Mobility, Trade and Control at the Frontier Zones of the Carolingian Empire ( 8^th–9^th Centuries AD ) *

1. Introduction: Frontier Zones and Empires

There were a great variety of borders and frontiers in the Early Middle Ages, many of which intertwined and even overlapped with one another. Indeed, medieval frontiers encompassed not just military and political borders, but also the fragmented complexity of cultural, ethnic, religious and economic differences. During the eighth and ninth centuries, the Carolingians directed their efforts towards the peripheral regions of the kingdom to both combat threats from neighbouring kingdoms and peoples and to expand their realm. The great expansion of the eighth and the early years of the ninth centuries began with the reconquest of all the territories that had once been part of the Merovingian kingdoms, under the leadership of Charles Martel and his sons, Pippin – the future king of the Franks – and Carloman. The expansion then continued with the constant state of war that took place under the reign of Charlemagne ^[1]. As a result of these conquests, the Frankish kingdom expanded its borders to its maximum extent, incorporating into the Carolingian dominion the Lombard kingdom in Italy, the Saxons in northern Germany, a strip of land beyond the Pyrenees on the Iberian Peninsula, the Istrian Peninsula, the Dalmatian mainland, and some territories once controlled by the Avar Empire in the region that Frankish sources call Pannonia ^[2].

One classic approach in the history of empire is to focus on imperial peripheries to understand how the relationship between the imperial centre and the margins functioned ^[3]. Ever since Frederick Jackson Turner published his famous essay on the American Western frontier, medieval historians have analysed the long Middle Ages through the lens of the frontier and Turner’s so-called ‘frontier thesis’ ^[4]. From the second half of the twentieth century, and especially from the beginning of the new millennium to the present day, there have been numerous studies on the shape, the perception, the archaeology, the impact and the complex intertwining of the different realities that overlapped in early medieval frontiers ^[5]. As political entities that by definition claimed a greater or lesser degree of universal and ecumenical afflatus, empires are key to understanding peripheries, marginal areas, borderlands and borders, what historians prefer nowadays to call frontier zones. In fact, at the borders of empires, the paradox arose whereby a state entity declared itself as the ruler and order-giver of the entire world yet had to set limits to its own aspirations ^[6]. Sometimes these political, cultural, economic and military limits even manifested themselves in the form of military structures such as fortresses, watchtowers, customs posts and walls. Even the Early Middle Ages have their own examples of ‘walls’: large linear earthworks, like the Danevirke, close to the Frankish and Danish border, and Offa’s Dyke, built by Offa, king of Mercia, on the border with Wales ^[7].

Even before Charlemagne’s famous Christmas coronation in Rome in 800, the Frankish kingdom could have been called an ‘empire’ by modern definitions. The Frankish kingdom, in fact, was a “complex trans-ethnic and trans-regional political network” that, like most empires throughout history, caused changes on its fringes through expansion, which reshaped local power-relationships and introduced new ideological discourse ^[8]. Frankish aspiration to world domination, whether ideal or actualised, was infused by a strong Christian missionary purpose ^[9]. This strong Catholic – and therefore universal – belief in an imperium christianum sine fine clashed with the harsh reality of the surrounding world. Indeed, some neighbouring peoples remained pagan, such as the Danes and the Slavs, or Muslim, such as the Saracens and many other peoples of Iberia. Moreover, not all the Christian peoples of Europe were fully integrated in the empire; these include the Lombards of southern Italy, the Bretons, the Venetians, the various peoples living in the British Isles, and most of the cities on the Balkan shoreline on the Adriatic Sea. Nevertheless, as Mayke de Jong has pointed out, “in the territorial sense of the word, this empire ended where the correct Christan cult was no longer practised. Its boundaries were liturgical as well as political: the right kind of baptismal rite determined membership of the political community.” ^[10] This strong sense of a divine mission is more evident in the years of Louis the Pious than during the reign of his father Charlemagne ^[11]. The proposed universality was therefore to be achieved through the conquest and conversion of neighbouring peoples, to integrate them, assimilate them and make them one with the Franks themselves. As Einhard optimistically wrote, after the end of the war, Franks and Saxons became one people in Christ: Christianae fidei atque religionis sacramenta susciperent et Francis adunati unus cum eis populus efficerentur ^[12]. The case of the Carolingian Empire is thus a good example of how despite theoretically and ideologically claiming supremacy over the whole world ( orbis terrarum ), imperial powers must compromise with the reality of their peripheries if they want to rule them. Hence, empires usually adopt a pragmatic and compromising policy towards their peripheries to avoid the possibility of a permanent state of war with local elites and populations, especially those recently subjugated and very different from those in the centres ^[13].

The great investments in terms of political and religious capital, manpower, and military efforts that the Franks dedicated to the peripheries were also aimed at reinforcing the control of the king and the ruling elites in areas where, usually, the influence of the central authority was weaker and more difficult to impose ^[14]. As Julia Smith and other scholars have stressed, the Franks exerted their influence over the newly conquered territories with a practical approach, establishing compromises with local powerbrokers and alternating violence and diplomacy ^[15]. The great variety and complexity of the frontier zone obliged the Franks to adapt their strategy to local circumstances. In a pragmatic way, the Franks were able to alternate the use of the sword, or the menace of it, with diplomacy and a readiness to accept and integrate lifetime enemies into their elites. This happened, for example, with the two Saxon leaders Widukind and Abbi, who were fiercely fought for years by the Franks, and then, once defeated, were baptised and accepted into the Carolingian ruling elites ^[16]. As Alcuin of York wrote in one of his letters, some Saxons were converted and coopted “by gifts, and others by threats.” ^[17] As highlighted by Ingrid Rembold, this process of integration and cooptation is still evident in sources some decades after the end of the Saxon War. For example, around 860–870, Waltbrath, Widukind’s grandson, was the dedicatory of Rudolf and Meginhard of Fulda’s ‘Translatio Sancti Alexandri’ ^[18]. This text, as well as other translationes written in Saxony during the ninth and tenth centuries, provided an account of the Saxons’ participation in the wider practice of translating relics in the Carolingian empire, a ritual process of relic discovery and exchange that linked together regions and peoples of the empire, and redefined the identities of local elites and peoples in connection with the Franks and the Carolingians as well as the wider catholic community ^[19]. Relics were traded, bought and stolen throughout the vast Mediterranean world; and the movement of saints’ relics as well as the involvement of public authorities in this process were already extremely developed by the ninth century. The very intense mobility of relics between Saxony and Italy, and their strategic appeal as sources of power, prestige, self-representation and religious authority, was thus an important mark of Saxon integration into the empire.

Nonetheless, violence and conversion – often forced – were not enough to pacify and rule Saxony. Therefore, the Franks depended on forging alliances with the local elites. Admittedly, peripheries, as explained by Timothy Reuter, were the places where the same elites could get rich through looting and tributes, thanks to a constant state of pillaging, raiding and victorious warfare ^[20]. But frontiers were not places where violence and conflict were the only norm: they were also places of a vibrant exchange of goods and ideas, where merchants, royal envoys, missionaries, craftsmen and people from other parts of the world met and communicated ^[21]. At the frontier zone, the Carolingians were even able to answer Muslim requests for aid, as Charlemagne did for Sulayman al-Arabi at the Paderborn’s assembly in 777 ^[22], or to accept pagans as faithful servants, as Louis the Pious did in 814 with the exiled Danish prince Harald Klak ^[23]. Another way to rule the periphery and to impose Frankish authority on the territory was to christianise the defeated peoples, as happened in Saxony and in Pannonia ^[24]. After the destruction of the Avar Empire, the Carolingians organised the so-called ‘Conventus episcoporum ad ripas Danubii’, a council deciding how to christianise and convert the newly conquered peoples and territories ^[25]. The ‘Conventus episcoporum ad ripas Danubii’ explains the urge that Carolingian elites felt to re-organise, standardise, and absorb the frontier zone ^[26]. The Frankish management of the border zones, therefore, while equal and uniform in the field of political theory, was in fact different from region to region, varying in intensity, military presence and policies. Nonetheless, the aim of frontier management was always to impose Carolingian authority.

This contribution investigates the practical aspects of these impositions, by analysing the legislative, military and infrastructural measures taken by Frankish authorities in the early ninth century to control and regulate the movement of goods and people across the northeastern borders of the empire, then comparing it with practices in Lombard Italy and other earlier examples of movement control. The Capitulary of Diedenhofen and its information on the Elbe frontier offers the unique opportunity to do so, and to study the relationship between imperial control over the frontier and the construction of new infrastructure. The various measures to oversee the frontier zone of the Elbe will then be compared to those taken on other peripheries of the Carolingian Empire. From this, I will suggest that the various practices of control were possible only if adequately accompanied by logistical and military infrastructure, and thus that selectively allowing and denying, and monitoring mobility across borders was a widespread practice in the Early Middle Ages ^[27].

2. The Border Zone of the Elbe River and the Capitulary of Diedenhofen

The management and control of the mobility of goods and people was a tool of fundamental importance, with which kings and elites could impose their power on the surrounding territory ^[28]. Control of the merchants was a prerequisite for the collection of tolls and thus for the acquisition of economic and political power ^[29]. Indeed, one of the first initiatives taken by the Franks at the end of the long war against the Saxons from 772 to 804 addressed the control of mobility and the creation of an infrastructure network in the area. However, one of the most interesting sources regarding the management of the Carolingian border zone is Chapter 7 of the Capitulary of Diedenhofen. This capitulary was issued in the palace of Diedenhofen, today Thionville in the department of Moselle, France. Charlemagne arrived in the villa with his retinue in July 805 after hunting in the Vosges Mountains ^[30]. Charles the Younger then joined his father after a victorious military campaign against the Slavs fought in the same year. As the ‘Annales Mettenses Priores’ and the ‘Chronicon Moissiacense’ report, this was an important campaign fought on the eastern border of the empire. In fact, three armies were set to invade the land of the Bohemians. Charles the Younger entered the “territory of the Slavs called Bohemians” from Germany ^[31]. Another army, composed by Saxons and Slavic tributaries, was ordered to enter Bohemia by the northern route, while an army of Bavarians marched in from the south-west ^[32]. It was after this devastation of the land of the Bohemians that Charles the Younger joined his father in the Vosges, and then the two Charles moved together to Diedenhofen. There, before Christmas, King Pippin of Italy and King Louis of Aquitaine arrived. The assembly of Diedenhofen was thus destined to be a decisive moment for the present, and for the future of the empire and the regnum Francorum et Langobardorum. In addition to the capitulary, which I will discuss shortly, more complex issues were to be discussed, including the division of the empire between the emperor’s three eldest sons and, consequently, the reconfiguration of the networks of power revolving around the three Carolingian kings and the spatial reorganisation of the empire ^[33]. It was during this important assembly that Charlemagne issued the double capitulary of Diedenhofen ^[34].

The capitulary was split in two parts, the first one about ecclesiastical and lay matters, while the other addressed the missi of the kingdom, and other general matters. One of the first topics of the second part of the capitulary was the dangerous famine of 805. To overcome the situation, Charlemagne ordered that “[ … ] each person is to help his own people as best he can and is not to sell his corn at an excessively high price, and no foodstuffs are to be sold outside our empire.” ^[35] Then, in chapter 7 were listed the only inhabited centres where it would have been possible to trade with the neighbouring Slavs and Avars:

[ ch. 7 ] Concerning the merchants ( negotiatores ) who are going to regions of the Slavs and Avars, and they must proceed with their business, that is, to the parts of Saxony as far as Bardowick, where Hredi is in charge; and at Schezla where Madalgaudus is in charge; and at Magdeburg where Aito is in charge; and at Erfurt where Madalgaudus is in charge, and at Hallstadt where Madalgaudus is also in charge; at Forcheim, and at Premberg and at Regensburg Audulfus is in charge, and Warnarius at Lorch. And let them not bring weapons ( arma ) and armour ( brunias ) to be sold; and if they be found carrying them, that all their goods should be taken away from them, one half to the share of the palace, and the other half shall be divided between the above-mentioned missi and the person who found out ^[36].

As we can see from the text mentioned above, on the northeastern borders of the empire, from the North Sea to the Danube River, Charlemagne enacted a series of rigorous policies that were aimed at effectively directing trade towards fortified centres that were managed by royal envoys. Additionally, the Carolingians made the trading of weapons and armour illegal, thereby ensuring that these commodities did not fall into the hands of neighbouring peoples, such as Avars, Slavs and the Northmen. This strategic decision not only helped control and promote commerce, but also maintained peace and stability within the realm ^[37]. Even if “economic and social resources available at that time were not sufficient for supporting cultural uniformity across the entire area under the direct control of the Carolingians [ … ]” ^[38] as Joachim Henning wrote, the Franks invested in the eastern borderlands to create new infrastructure and trade centres to absorb this wide region into the empire. In the peripheries, the Carolingian government established new symbolic spaces of power by controlling the movement in and out of border areas, and imposing restrictions on the trade of specific goods. This was a crucial aspect of their governance at the frontiers.

One of the main purposes of the capitulare was to regulate the trade in and out of the eastern frontier zones of the Carolingian empire, which had to be controlled to ensure security in a high-risk peripheral region. The places mentioned in the text, which extend from the North Sea to the Danube and were mostly settlements or villages located close to rivers near the border, were the only places where trade with Slavs and Avars was permitted ^[39]. Three of these trading nodes, Bardowick, Schezla and Magdeburg, were in Saxony. The others were Hallstatt, Erfurt, Forcheim, Regensburg, Lorch and Premberg, and were distributed between Hesse and Bavaria, with the furthest at Lorch along the Danube in present-day Austria ^[40]. The Capitulary of Diedenhofen also names the various royal envoys to whom the administration of commercial hubs was delegated. This is a broad region that includes the mouth of the Elbe river in the North Sea, near the city of Hamburg, then it follows the course of the Elbe and Saale rivers. After Forcheim, the frontier zone passes through Bavaria and then, from Regensburg on, it follows the course of the Danube up to Lorch. As highlighted by Matthias Hardt, all the places listed in the Diedenhofen capitulary were located at the crossroads of land and river routes, or at the mouth of smaller rivers through which the area of Slavic settlements could be easily reached. Bardowick, for example, was an important trade place, and Magdeburg later became a prominent center under Henry the Fowler and the Ottonian dynasty ^[41]. Of all these places only Schezla has not yet been clearly identified ^[42].

It is interesting to note that none of the above-mentioned places were used by Charlemagne or Louis the Pious as gathering or assembly centres. After the last assemblies held by Charlemagne in Saxony in 804 ( Lippspringe and Hollenstedt ), Louis the Pious held one sole assembly in Paderborn in 815. Only under the Ottonian dynasty would there be a flourishing of assemblies in the Elbe and Saale region ^[43]. As demonstrations of supremacy and triumph, assemblies were an important part of Frankish dominion. It is not surprising, then, that most of the assemblies organised by Charlemagne, as Caspar Ehlers states, “took place in Westphalian localities between the river Rhine and Weser that had been secured early on.” ^[44] The Elbe region, recently conquered and reorganised by the Diedenhofen capitulary, required particular political and military attention since the menace of neighbouring peoples was still very strong in the region. The situation of trading posts at these sites must therefore be linked to and studied in conjunction with the significance of these sites as actively negotiated frontiers, distinct from the centres of authority from which assemblies were held. This is demonstrated by the continuous incursions of the Frankish army into Slavic territories during the reign of Charlemagne, and, later on, by Slavic and Danish incursions into Frankish lands during the reign of Louis the Pious. The constant state of warfare, both aggressive and defensive, helps us to understand the promotion of these royally-controlled centres of trade, and the structural efforts made by the Franks from 806 onwards. The Franks had to organise the frontier zone and trade over the border so as to protect not only trade and merchants, but also the inhabitants of the region.

Another important aspect of this capitulary for understanding Carolingian policies in the border areas is the prohibition of selling weapons and armour to Slavs and Avars. This limitation on commerce, which is stressed in the capitulary of Diedenhofen ( “they should not bring weapons and armour to be sold” ), mirrors similar limitations that were already implemented in earlier capitularies ^[45]. Those caught trading weaponry to neighbouring peoples with whom commerce of these goods was forbidden would be punished with the confiscation of all the goods in question. In order to motivate and encourage the perquisitions of merchants, half of the contraband goods would have gone to the officials in charge, the other half to the king ^[46]. This decision echoes one already taken in the ‘Capitulare Haristallense’ of 779, issued by Charlemagne, where one reads: “About armour, that none should presume to sell it outside our kingdom.” ^[47] This specific capitulary was written in the middle of the Saxon war, while Charlemagne was still facing strong opposition in Westphalia and in the valley of the Lippe River. The general prohibition on selling armour ( brunias, there is no mention for arma, as in the Diedenhofen capitulary ) of the ‘Capitulare Haristallense’ of 779 was later made more specific in the 805 capitulary of Diedenhofen ( “And let them not bring weapons [ arma ] and armour [ brunias ] to be sold” ) ^[48], which also bans selling weapons and armour to specific groups, the Slavs and Avars. After 804, the Saxons were no longer a problem. The last rebellious Saxons had, in fact, been deported, and the capitulary emphasises that the real menace now came from the neighbouring Slavs, the Danes and the remaining and dispersed Avars in the Danube basin.

This prohibition on the sale of swords outside the kingdom, repeated in several capitularies, did not mean that Carolingian weapons never circulated beyond Carolingian borders. On several occasions, archaeologists have found Carolingian-made swords in territories beyond the frontiers. Frankish swords have indeed been found in Slavic territory ^[49]. They may have been sold by Frankish merchants before the Diedenhofen ban, or smuggled in after it, or were the spoils of a battle in which the Slavs had prevailed. There was a huge trade in weapons in Carolingian Europe, as evidenced by finds from the port town of Dorestad, in present-day Netherlands, near the modern town of Wijk bij Duurstede. The discovery of numerous swords here suggests that they were not only forged and used by the city’s guards, but also the object of a vast trade with the rest of the Frankish world and the North Sea emporia ^[50]. The importance of this commerce, and the rise of trading places in the North Sea such as Hedeby, Dorestad, London, and Birka, is also underlined by a passage in the Royal Frankish Annals where Godfrid, king of the Danes, during his invasion of Obodrites lands in 808, ravaged and destroyed the port of Reric, taking with him into the coastal city of Hedeby all the merchants that were living there ^[51]. A similar limitation to the one of Diedenhofen was already defined in the ‘Capitulare Mantuanum’ of 781, issued in Italy, in which the ban on selling weapons outside the kingdom ( foris regno nostro ) ^[52] was added to the ban on selling Christian or pagan slaves. In the capitulary of Diedenhofen, however, there is also the injunction not to export grain outside the kingdom ( ne foris imperium nostrum ) ^[53], made in response to a famine. Analogous bans help us to better understand the Frankish effort to oversee the border area, and to prevent neighbours from buying Frankish arms and armour, probably of better quality, thus becoming a possible threat to Carolingian interests across the border zone ^[54]. All this regulation went hand in hand with the building of fortresses, bridges and infrastructure, at least where older buildings did not already exist, to guarantee the defence of the territory and the successful control of its merchants. In the Early Middle Ages, the protection of merchants, resources and technologies, and internal trade ( including its expansion as well as its defence ) were priorities for the central authorities in both Frankish and Danish lands ^[55].

The second part of the Diedenhofen Capitulary should hence be read as supporting evidence for greater Carolingian political and military activity than has been acknowledged in the eastern frontier zones. Even after the defeat of the Saxons ( 804 ) and the Avars ( 796 ), the northern and eastern border regions of the Carolingian empire were still dangerous territories, as proved by the deaths of two important high-ranking officials of the empire: Gerold, praefectus of Bavaria, and Eric, duke of Friuli ^[56]. The Franks fought against several peoples along those borders. On the other side of the border zone, confederations and kingdoms of Slavic peoples such as the Bohemians, the Sorbs, the Linones, the Carantanians, the Slavs of Lower Pannonia, and the Wilzi, were difficult to subjugate. The threat of the Danes in the north grew stronger from 808 onwards. In 805, Charles the Younger fought against the Slavs in Bohemia, and in 806 he led another army against the Sorbian Slavs while an army of Burgundians, Alemanni and Bavarians ravaged the Bohemian region ^[57]. From 808 onwards, the presence of the Danish king Godfrid became a real threat to Carolingian sovereignty in the Elbe region ^[58]. Godfrid defeated the Obodrite Slavs, allies of the Franks, on multiple occasions and imposed his authority in this region between the Danish Kingdom and Saxony ^[59]. Indeed, these multiple threats obliged Charlemagne, and later his son Louis the Pious, to build forts on the two sides of the Elbe to protect Frankish interests in the region ^[60].

3. Building on the Frontier Zone

Following the end of the Saxon conflict in 804, and the deportation of thousands of Nordalbingian Saxons to Francia, the Franks undertook the construction of infrastructure along the banks of the Elbe to control the surrounding region and defend the recently conquered territories. The distance from the heart of the kingdom, the lack of Roman infrastructure, and the threat from the Slavic populations beyond the Elbe were just some of the reasons that influenced the Franks to build various fortresses in this region. From 805 onwards, Charlemagne engaged himself in the reorganisation of the Saxon lands, paying great attention to the periphery of the Elbe and Saale rivers. The settlement of the Obodrites, even defined by the sources as Sclavi nostri, “our Slavs” ^[61], in the territory that was once inhabited by the Nordalbingians and that now separated the Danes from Frankish Saxony, was later followed by the Capitulary of Diedenhofen, and by the reorganisation of the entire eastern frontier of the Carolingian empire. However, the control of goods and of mobility across the border area could only be guaranteed by creating physical structures capable of implementing these rules. The year following the Diedenhofen capitulary, the Franks built two fortresses, one on the western bank of the Saale River and the other on the eastern bank of the Elbe ^[62]. This second fort was built in front of Magdeburg, one of the commercial nodes already mentioned, governed by the missus dominicus Aito, as the author of the ‘Chronicon Moissiacense’ recalls ^[63]. Magdeburg’s position was strategic, since it was both one of the trading points indicated in the Diedenhofen Capitulary and also because it was located on one of the main routes connecting Saxony to the Slavic territories ^[64]. However, the fort was not built in the centre itself, but on the opposite side of the river ( ad aquilonem partem Albiae contra Magadaburg ^[65] ), so as to guarantee greater defence for the bridge that linked the two banks and to allow the passage of merchants ^[66].

In 808, the emperor ordered that two of his envoys build two fortresses on the Elbe to defend themselves against the attacks of the Slavs. According to the entry in the Royal Frankish Annals for 808, “[ a ]fter having two castles built on the River Elbe by his envoys and placing troops in them for the defense against the attacks of the Slavs, the emperor spent the winter at Aachen [ … ].” ^[67] One such fort was most likely the one later described as “the castle of Hohbuoki” ^[68] in the Royal Frankish Annals, built on an island in what is now called Hannoversches Wendland ^[69]. Hohbuoki fort was later captured by the Wilzi, who in 810 captured the Franks residing there along with Odo, the imperial envoy in command of the Franks that defended the fort ^[70]. In the same years, Charlemagne also had a fort built at Esesfeld, in what is now the southern part of Schleswig-Holstein, on the river Stör, in a strong position to counter Danish incursions in this area and protect the city of Hamburg at the mouth of the Elbe. A count named Egbert was sent to build the fort of Esesfeld, located 14 km north of the Elbe and 60 km south of the Danish Danevirke, near the present-day city of Itzehoe ^[71]. This building activity did not stop with the death of Charlemagne and shows how Louis continued his father’s policies in the Elbe region. In 822, the emperor Louis the Pious had the Saxons build a fort at Delbende with the declared intention of defending themselves against the attacks of the Slavs: by then the Obodrites were no longer “our Slavs” as they had been during his father’s time, and the border area was more exposed than before ^[72].

The development of a well-structured system of fortresses and trade centres on the north-eastern frontier zone under the leadership of the royal missi was beneficial to the defence of the newly conquered territories, and the development of the region. This building process coincided with the development of a Christian landscape in the newly submitted areas of Saxony. A key feature in the conquest of Saxony, as well as in the war against the Saxons, was the missionary aspect of converting pagans ^[73]. In fact, the process of conversion received a great boost during the thirty years’ war that the Franks waged against the Saxons ^[74]. The conquest and subjugation of the various Saxon tribes went hand in hand with their – often forced – conversion. Laws such as the ‘Capitulatio de partibus Saxoniae’ ^[75], the ‘Capitulare Saxonicum’ ^[76], or events like the massacre of Verden ^[77], and the debate raised by Alcuin of York on the usefulness of the tithe to be paid to the newly founded ecclesiastical institutions imposed on all Saxons ^[78], illustrate the harshness and uniqueness of the conversion of the Saxons ^[79]. While conquering and converting the Saxons, the Franks built numerous churches and monasteries, and established bishoprics to govern the territory and ensure the complete christianisation of the land and its inhabitants. As Ingrid Rembold writes, the creation of a Christian landscape in Saxony was not a straightforward process ^[80]. However, towards the end of the eighth century, some diocesan sees were already founded ^[81]. Since there was a general lack of cities in Saxony, many of these religious centres were founded at fortified sites, as demonstrated by the missionary centres and bishoprics of Bremen, Verden, Osnabrück, Paderborn, Münster and Minden ^[82]. The construction of churches, the imperial palace at Paderborn ^[83], bridges, monasteries, markets, and other buildings surely attracted a large number of artisans and workers from other regions of the empire to Saxony, with a growing need for construction materials, goods and other necessities to be purchasable through trade. These nascent ecclesiastical institutions, then, were not only a missionary force, but most likely also acted as royal agents in the area, capable of controlling the surrounding region and the newly subjugated population, and yet dependent on trade and infrastructure for their continued existence.

4. Practices of Frontiers Control: A Comparison Between Lombards and Franks

Controlling, directing, and preventing the mobility of peoples and goods were not practices unique to the Carolingians or the Franks. Indeed, scholars have highlighted that restrictions such as those imposed by the Franks on trade and circulation were not uncommon between the eighth and ninth centuries. Already in the second half of the eighth century, the Lombards introduced custom stations called clusae to control the movements of peoples across the Alps and prevent an easy alliance between the Carolingians and the pope. The clusae did not achieve their goal, and they fell into disuse until their later restoration by King Pippin of Italy, Charlemagne’s son. Yet, despite this, and the distance in time and space, it is useful to compare Lombard laws about the clusae and movement across the marca, as they called the frontier zone, with those issued by Charlemagne in 805 ^[84].

The Lombard kings Ratchis and Aistulf established customs posts, called clusae, located at Alpine passes, that were intended to supervise movement through the Alps in the first half of the eighth century ^[85]. Their successor, King Desiderius, had the clusae restored in preparation for a conflict with Charlemagne and the Franks. According to the laws of Ratchis ( 744–749 ) and Aistulf ( 749–756 ), the clusae, located along the transit routes of the Alps, were places to control anyone who crossed the frontier of the kingdom. This control was to be performed through the use of an official recognition, a document delivered at the border by the guards in charge – called clausarii – who would then collect the same document when the traveller left the kingdom ^[86]. These structures, as Walter Pohl has explained, were not only the answer to a moment of great political crisis for the Lombard kingdom, but also a means of internal control and defence against outsiders in times of peace ^[87]. In fact, the aim of the laws about the clusae was to control movement through the realm. The text of Ratchis’ law explained how those who pass through the checkpoints must be stopped, to know who wants to enter or leave the kingdom: “[ … ] but no man should enter through the border without a sign or a letter from the king.” ^[88]

Controlling the Alpine crossings and passes was fundamental for the Carolingians too, in order to project Frankish power beyond the mountain range, and into the Lombard kingdom. Before the conquest of the Lombard kingdom, the Franks also organised themselves to control movement across the Alpine passes. Most likely, this organisation was the response to previous problematic episodes, as the Frankish-Lombard history reminds us ^[89]. In a passage of the ‘Annales Mettenses Priores’, Grifo, the half-brother of Pippin who was excluded from Charles Martel’s inheritance, was intercepted at Saint Jean-de-Maurienne by Theodowin, Count of Vienne. Count Theodowin was one of King Pippin’s faithful and, with his men, responsible for the defence and control of the Alpine passes ^[90]. According to the passage, Grifo was trying his luck at entering the Lombard kingdom, after having been driven out of Bavaria the previous years by his older brothers. However, he was intercepted by Theodowin and killed in battle. We can thereby assume that the task of these men was to control the mountain passes and crossings on the Frankish side. Count Theodowin and his men, in fact, were described as those who “guarded the crossing of the Alps”, qui Alpium transitus tuebantur ^[91]. Although not organised, as far as we know, like the clausarii and clusae of the Lombard laws, Count Theodowin and his men had to control transit across the Alps, an essential passageway for pilgrims and merchants. Unfortunately, unlike the codified Lombard laws concerning the Alpine clusae, there are no written documents that clarify how the Franks guarded and controlled their Alpine passes and frontier routes at the time of Count Theodowin and King Pippin III. However, as Gianmarco De Angelis notes, controlling mobility across the Alpine passes is the purpose of a legislative measure taken later by Pippin, son of Charlemagne and king of the Lombard kingdom, in 787 ^[92]. In a moment of tension between the Bavarian duchy and the Frankish kingdom, Pippin ordered the re-establishment of controls at the entry points ( portas ), together with identification documents ^[93]. The importance of the transit routes and control of the Alpine valleys is also underlined by the fact that, in planning the attack against the Duchy of Bavaria in 788, King Charles ordered his son Pippin’s army to march towards Trento, and then move on to Bolzano, thus securing the Brenner Pass up to the Resia Pass ^[94]. The fact that King Pippin of Italy ordered the re-establishment of control measures in the Alpine passes allows us to hypothesise that once the Lombard kingdom was conquered by Charlemagne, the system of the clusae and the control of the movement across the Alps was slowly abandoned. Since from 773 onwards, both sides of the Alps were under Frankish domination, supervising mobility across the Alps demonstrates that this practice was mostly conceived for times of struggle and danger for the kingdom, whether Lombard or Frankish.

The Franks knew of the Lombard system of the clusae, but why did they not use it on the northeastern border zone of their empire? The answer, from my point of view, is twofold. Firstly, creating an organisation like that of the clusae on the Elbe and Saale rivers would require a system of infrastructure capable of controlling the main routes that went through the frontier. The Lombards in the Italian Peninsula, and later the Franks, were able to utilise old Roman roads, towers, fortifications, and infrastructure. These buildings were missing in the Elbe region and the Franks were compelled to build them from 806 onward. Secondly, the topographical differences between the narrow Alpine passes and the wide rivers, swamps, plains and forests of the region that goes from the North Sea to the Elbe, Saale and Danube rivers made it more difficult to control the region surrounding the Elbe. Passages and roads through the Alps were mostly obliged to utilise certain places and valleys, while on the Elbe there could have been multiple places to cross the frontier ^[95]. Another possible explanation for the difference between the clusae and the system of control implemented along the Elbe River is the use of written documents. On the northeastern frontier it was probably sufficient to control goods rather than people, as was the case with the Lombard clusae. At the same time, it should be stressed that there was a different tendency towards the written document. There was certainly a greater familiarity with written documents in Lombard Italy than in the Frankish tradition of border control, as the vagueness of Count Theodowin’s role attests. Therefore, the objective of the Capitulary of Diedenhofen was to protect the kingdom from external threats while organising a wide territory, creating a new topography of power that could impose Carolingian authority in a wide frontier area which stretched from the North Sea to the Danube River. What interested both the Carolingians and the Lombards more than the fortifications of the passes for defensive measures, was the control of transit routes, the valleys and the Alpine passes.

Monastic and ecclesiastical institutions were also used to control mobility. Monasteries, often built near important routes, played a strategic role in controlling the surrounding territories and the peripheries. Nor should we underestimate the economic, cultural and social impact that these institutions had on the territory in which they were founded ^[96]. Monasteries were centres of spirituality and culture, through which institutions, both religious and secular, could consolidate their hegemony over the surrounding area, thus guaranteeing a trusted intermediary in peripheral and difficult-to-control regions ^[97]. Indeed, the position of the monasteries had great political importance, as in the case of the abbeys of Novalesa, Nonantola, San Salvatore, Monte Cassino and Farfa, all built in frontier zone territories of the Lombard kingdom ^[98]. It is in light of these considerations that we must read the political initiatives and donations made by Charlemagne in the years immediately following the conquest of the Lombard kingdom ^[99]. For example, in a diploma issued in Pavia on July 16^th 774, Charlemagne and Queen Hildegard donated the entire Camonica Valley to Abbot Gulfrado, acting in the name of the Monastery of Saint Martin of Tours ^[100]. The donation to the Monastery of Saint Martin not only rewarded the loyalty of a trustworthy and faithful institution, increasing its landed wealth, but also allowed indirect control of a key region for mobility along the Alpine arc ^[101]. In the same period, the Abbey of Saint Denis was also the recipient of a similar donation, being granted with the Valtellina, another important transit route for northern Italy ^[102]. As recently noted by Maria Elena Cortese, after the conquest of the Lombard kingdom, those were two of the most important mining districts in Italy ^[103]. Similar to the Italian case is also the incorporation of the important passageway of Chur through the placing of the people of Raetia and the church of Chur under Charlemagne’s mundoburdo vel defensione nostra ^[104]. This was another important passageway on the northern side of the Alps ^[105]. Through these actions, Charlemagne was able to control both strategical places and important economic resources. In the years of the capitulary of Diedenhofen and the organisation of the Elbe frontier zone, the Franks were still in the process of building a Christian landscape in Saxony. Although Christian ecclesiastical and monastic institutions already existed in the area, they were not as well established as in the rest of the empire. Nevertheless, these centres played an important role in spreading Carolingian authority and the Christian religion among the Saxons. In fact, bishoprics were established close to fortified centres that already ruled the surrounding countryside ^[106]. The fortifications along the Elbe and Saale rivers and the construction of new trading centres allowed these newly established ecclesiastical institutions to flourish. Hamburg, for example, became an important centre for the evangelisation of the Danes and Norsemen ^[107]. Nevertheless, Charlemagne’s main interest in the Diedenhofen Capitulary was to create a network of fortified commercial centres ruled by royal missi.

One of the many problems that the frontier zone posed for the central authority was how to impose control over the population, the local elites, the land, the resources, trade to and from the border areas, and the taxes and tolls levied on the resident population. To respond to these problems in the Elbe region, the Carolingians committed themselves in a pragmatic way by not only regulating trade, but also by guaranteeing the defence of the territory from external threats through the construction of a series of fortresses, while using the threat of force – or violence itself – and diplomacy to submit the neighbouring Slavic peoples. Also, as underlined in the Diedenhofen Capitulary, Charlemagne stated that the old and fair taxes should be respected, while the new and unjust ones, very often implemented locally, should not. This complaint can be better understood if we compare it to the well-known and studied Plea of Rižana ( 804 ) ^[108].

In the Plea of Rižana, the local population of Istria complained about the abuse of power by John, the Frankish appointed duke of the region. The Istrians claimed that the duke was abusing his power by implementing new tolls, imposing corvèes, and other taxes ^[109]. After an inquiry, the royal missi agreed with the local population and asked the duke to take an oath to not impinge on the population’s traditional rights. It is clear from this event that Carolingian governance of newly subjected peoples faced a fragmented reality that required pragmatic rulership, “balancing” it, as Julia Smith wrote, “between protecting Frankish interests and provoking an anti-Carolingian backlash.” ^[110] There were also numerous port customs, and customs stations that intercepted merchants moving on the roads of the kingdom, from north to south ^[111]. Thus, for example, the Lombard clusae of the Susa Valley, Aosta Valley and one near Chur were not only supposed to serve military purposes, but also to control the traffic of merchants entering and leaving Italy ^[112]. There were also customs on the French Mediterranean coast, probably at Marseille and Arles, as well as control stations along the great rivers of northern France, such as at Rouen ^[113]. As concerns the control or prohibition of movement and commerce more widely, the embargo that Charlemagne imposed on traders from Britain in 790 is also well known. Similarly, as Alcuin reports, Charlemagne ordered that no one from Britain was allowed to trade in Gaul after Offa of Mercia refused to arrange a marriage between his son, Ecgfrith, and King Charles’ daughter Bertha ^[114]. Mobility management thus became a fundamental instrument of power and authority. It made it possible to impose order on a frontier area with complex features, where alliances changed frequently and human, political, commercial and military interests overlapped with each other ^[115].

5. Conclusions

The control of mobility across border zones played an important role in the peripheries of early medieval realms such as the Lombard and the Frankish kingdoms. Carolingian rulers employed a combination of violence and diplomacy, as well as a policy of integrating defeated elites and incorporating them into their ranks. Following their military triumphs in Aquitaine, Saxony, Italy, the Danube basin and the Balkans, the Franks were faced with the challenge of establishing peace and order in the recently conquered lands. In order to achieve this goal, they used a variety of strategies. The new order established by Charlemagne on the north-eastern frontier zone at Diedenhofen did not create a fixed border from north to south-east. Instead, it created nodes of power, strategic places where Frankish authority was manifested by royal envoys, warriors, fortresses, guards, new ecclesiastical institutions and infrastructure. A fixed border would have, instead, blocked any Frankish adventure on the other side of the rivers. And, as we have seen, the Carolingians never stopped crossing the frontier and attacking neighbouring Slavic people. In fact, Carolingian power, echoing Walter Pohl’s words, did not create fixed boundaries, but opened up space for manoeuvre in which the outcome of the game was always open: Charlemagne’s priorities on the vast northeastern frontier were order and defence, but this wide region remained an open frontier ^[116]. As Mayke de Jong and Frans Theuws wrote, in the Carolingian borderlands of the Elbe, power assumed “different forms” ^[117]. Here, Carolingian authority had to weave new webs of relations between settlements, fortresses, royal envoys, local elites, trade centres, episcopal and ecclesiastical sites. Charlemagne thus issued new rules to control and manage trade and commerce. It is difficult to believe that across the wide frontier zone that went from the North Sea to the Elbe, Saale and Danube Rivers, only the few places listed in the Diedenhofen Capitulary were able to prevent smuggling, illegal trade and movements and other felonies. Indeed, the effort made by the Franks to control movement and mobility in other way is evident from the cases studied in this article. In his effort to establish Carolingian power over the Elbe region, Charlemagne thus used various tools like diplomacy and client management, violence and the fortification of geographical key-places – like Magdeburg –, and the issuance of laws to control, and to forbid commerce of specific goods through the borders.

In the various capitularies, we have seen that Charlemagne issued laws concerning trading and smuggling of illegal goods like weapons, armour, and also corn and “foodstuffs” ^[118]. These laws were usually implemented in situations of danger and war, like with the Saxons, or the Avars and the Slavs. At the northeastern frontier of the Carolingian empire, Charlemagne had to nominate one by one the various trading places and their missi, whereas in Italy, the Franks were able to use the Lombard clusae. I have argued here that this difference is in part due to the fact that in the Alpine valleys they were able to rely on Roman and Lombard infrastructure and institutions, while on the wide Elbe, Saale and Danube frontier zones, they had to create a new infrastructure of power to impose their authority. Similar problems were addressed with similar solutions in different environments. Through various investments in infrastructure, the creation of a relationship network with the defeated elites, the application of an ecclesiastical administration ( when needed, as in Saxony, or Pannonia, for example ), or the placement of trusted men in strategic places ( monasteries, duchies, cities and churches ), the Carolingians were able to build their network of power in the frontier zones ^[119]. From the fort of Esesfeld north of the Elbe River, via Bardowick, Hohbuoki, Schezla, Delbende and Magdeburg, the Franks built a series of fortresses, bridges and trading posts to protect their interests and their authority in the region. They built defensive and customs infrastructure, useful for trade and for the management of the peripheries. They did not barricade themselves behind the great rivers of central-northern Europe, but tried as much as possible to build on both sides of the Elbe, and to subjugate Slavic tribes that lived on the other side of the river. The aim was both to project their influence beyond the river, and to defend the recently conquered lands as much as possible and control the course of the river. These constructions, accompanied by the use of violence, diplomacy and the conversion and cooptation of the Saxons and neighbouring peoples, served to absorb a fragmented and disunited landscape. Carolingian infrastructural and political investments standardised the region into a network that served both political and economic interests. The Frankish buildings and new legislation implemented at the border zone of the Elbe river, therefore, served to mark the border areas and to materialise the new authority over the newly conquered territories in order to rule and control them.

In the specific case of the northern frontier between the eighth and ninth centuries, Saxony and the trading places of the Elbe region were key knots of great value for maritime and land trade that connected the various emporia of the North Sea and the Baltic Sea such as Hedeby, Dorestad, London, Reric and many others ^[120]. Commerce and the movement of people through the wide eastern frontier zone probably did not have the same volume as the one in the Mediterranean world, but it needed to be controlled ^[121]. Armours, weapons, luxury goods, grain, slaves, relics and other objects were not the only things that moved through the Carolingian frontier zones. It was therefore imperative for the Franks to control the land routes of trade, both for direct gain and to extend the range of their influence on both sides of the frontier. The peripheries in the Middle Ages were places where the efforts of the central authority manifested themselves through the construction of infrastructures and the organisation ( or re-organisation ) of the topography of power. The importance given to the control of movement to and from the border confirmed the importance of mobility, at the same time a threat, if not controlled, as well as an instrument of power, if adequately limited and addressed.

A Map of the North-Eastern Frontier of the Carolingian Empire, 8^th–9^th Centuries