The Carolingian and Ottonian Forification

Vikings – To Paris!

In general, there is little evidence of change or advances in fortification in northern and central Europe during the period between the collapse of the Roman Empire and the ninth century. The infrastructure of the Roman world did not exist and many of the Roman city walls fell into disrepair. In places walls were deliberately demolished, either for a ready supply of dressed stone or to make way for new structures. Settlements often moved to sites near the former Roman towns but outside the walls, as in the cases of York and London. Nevertheless, many of these returned to the former Roman sites in the ninth and tenth centuries, and in some places the Roman walls were still defensible. In 946 they proved too much for the combined armies of King Louis IV and King Otto I, who abandoned their siege of Senlis (defended by the troops of Hugh Capet, later the first Capetian king of France) after deciding that an assault would be too costly. In 985 King Lothar (of France) had to use an arsenal of machines and a siege tower to overcome the third-century walls of Verdun. In the previous century the same walls had saved the city from sack by the Vikings.

During the Viking Era fortification became much more widespread and previously undefended trading emporia were given defenses. An obvious explanation for this might be the advent of large-scale raiding by the Vikings and later the Magyars. Italy was also part of the Frankish world after 774 and suffered heavily from Saracen raids and later invasion. Undoubtedly this was a contributory factor, but there is evidence of a change in attitude in the Frankish Empire before the ninth century. The Carolingians made a conscious effort to imitate Rome, and this included Roman architectural styles, and their conquests brought them into close contact with Byzantine fortifications in Italy, themselves descended from the Roman model.

The Franks needed new forts to secure their hold on conquered territories. In areas formerly controlled by the Romans, such as southern Germany, earlier fortifications were certainly reused and repaired, but the defenses of these sites have often been difficult to date, if they have been researched at all. Former Roman villae were also used both by the Agilolfing dux Tassilo (r. 747–788) and by his Frankish successors in Bavaria. Until very recently it was wrongly assumed that Frankish and Slavic fortifications could be differentiated on the basis of style, the assumption being that the Franks built more advanced defenses from stone. Many of the early fortifications on the eastern frontier with the Slavs were of similar type to their enemies’. The construction of what became a deep belt of fortresses began in the Carolingian period and continued under the Ottonians. In Germany during the tenth century a huge building programme was begun under the Saxon dynasty. This may have been initiated by Henry I’s Burgenordnung of c. 925, although it has proved very difficult to link any known fortifications with it. The style of fortification on the eastern frontier varied. One object was certainly defense of rural settlements against raiders, particularly the Magyars, but also the Slavs. In the reign of Otto II similar defenses were organized on the comparatively short Danish frontier.

The Viking threat posed an altogether different problem than frontier raids by the Slavs, not least because the Vikings were capable of penetrating well inland up navigable rivers. An interesting solution to this problem was attempted by Charles the Bald. Carroll Gillmor suggests that the idea may have struck him when he built a bridge across the Marne to block the retreat of some raiders. When he held an assembly at Pitres in 864 he ordered the building of fortifications on the Seine to prevent the Northmen from passing further upriver. The idea was a bridge with powerful fortifications of wood and stone at each end. The site was Pont-de-l’Arche. Excavation has revealed a square enclosure with 270 meter-long sides on the north bank. Originally there was a clay rampart, but this was cut away to place a line of 4.5-meter tree trunks, which were then faced with stone on the outer side. Unfortunately there is no way of knowing the height of the work, as it was leveled in the later Middle Ages. The earth and timber rampart with stone facing was no more advanced than many fortifications had been in the Iron Age, but a more serious problem may have been that it was built very slowly and not properly garrisoned, despite the king’s demands. Another work was built at Les Ponts-de-Cé on the Loire, but that seems to have been ineffective as well. Elsewhere Charles did contribute to the defense of the realm. In his reign and those of his successors Carloman and Charles the Fat, many old walls of towns were repaired and new fortifications built round monasteries, including St. Bertin, which subsequently saw off a Viking attack in 891. However, it was not only the king who began to build forts, although this was supposed to be a royal prerogative. Although Charles had ordered the destruction of private fortifications at Pitres, he was unable to prevent unauthorized construction and a dangerous trend (from the royal point of view) had begun.

Similar measures against Viking attacks were taken on the Rhine and Meuse in East Francia after Danish attacks in 863, 880–881 and 884–885. Town defenses were strengthened, the royal palace at Nijmegen was given ramparts, and a castle was built by Duke Henry at Duisburg. In Flanders, more or less an independent polity at this time, Bruges and Ghent were fortified by Count Baldwin. Most interesting in this region, however, are five ninth-century circular earthworks with palisades on the islands off the coast of Zealand–Flanders. They had two roads across the site, meeting at the middle, and varied from 144 to 265 meters in diameter. Since no occupation layer was found, they were probably refuges. Only Middelburg on Walcheren survived this period to become a settlement. In the central Netherlands another unusual fortification was the Hunnenschans, a late Carolingian meter-high horseshoe-shaped earthwork with a palisade, enclosing an area 100 meters in diameter. In 2007 a further earthwork was discovered at Appel, just to the west, while to the south is another, Duno, with a roughly semicircular series of banks and ditches. Both appear to have been tenth century. There are uncertainties about the excavation and recording of data at Duno and Hunnenschans, but Appel at least seems to have had links to the counts of Hamaland and bog-iron production.

Fortifications also proliferated in the tenth century throughout the kingdom of Germany, and not only in the Slavic frontier zone, where there were hundreds of them. Many continued to resemble earlier Saxon, Frankish and Slav fortifications, while some were simple palisaded enclosures. Fortifications built by nobles often followed a similar pattern to royal ones, if on a smaller scale. There can be no doubt that there was a strategy of “defense in depth” on the eastern frontier. The East Frankish and German rulers were well aware that individual fortifications had a limited capacity to hinder the movement of enemy forces, just as they knew that it was difficult to stop enemy forces from “crossing the frontier.” Periods of intense construction of fortifications on the frontier appear to coincide with preparation for or consolidation of advances into Slavic territory, especially by the Ottonian kings, or anticipated trouble from the east.4 However, it has to be borne in mind that there were other reasons for fortification building. The kings of the Saxon Ottonian dynasty were keenly aware of the need to project their image and power as kings and emperors, and one way of doing this was to build imposing structures. Other powerful landowners also built fortifications for the same reasons; even if they were not able to compete with the German kings, they could still imitate them and compete with each other.

Many German scholars trace the origins of the “classic” medieval fortress types to the eleventh century, although the disappearance of many earlier fortifications has distorted the picture somewhat. The larger fortresses in Germany, often known as hohenburgen, had inner and one or more outer enclosures, not dissimilar in principle to many earlier German and Slavic fortifications. Whenever possible they were constructed on higher ground. However, a new development was the appearance of the Bergfried, a free-standing tower, either on the most vulnerable side of the main enclosure as an additional defense, or in the center of the enclosure and unattached to it. Usually the Bergfried was tall and slender and lacked windows; it was not designed for permanent habitation, but as a last resort if the main or outer defenses were overrun. Increasingly these fortifications were built or rebuilt of stone. According to Adam of Bremen, the archbishop of Hamburg planned to encompass the entire town of Hamburg with stone walls, but he died having built only a fortified stone structure with towers and battlements. This was certainly a response to the threat from the Slavs, which had increased after the revolt of 983. In 1008 Henry II also fortified Bamberg with walls, outworks and a strong tower. By contrast, the defenses at Meissen were probably made of wood, as the Slavs attempted to set light to them in 1015. Others were smaller, ringforts or square palisaded enclosures with or without a ditch. They too frequently included a Bergfried. Alternatively, towers could be built entirely on their own. Most were built of wood in this era, but stone towers were constructed on similar principles both before and after 1100. These towers were more common in low-lying areas, where they also fulfilled the function of watchtower.

The most significant change in fortification style in the eleventh century was the development of what we now call the motte-and-bailey castle, which originated in West Francia. It consisted of two elements, a mound (motte) surrounded by a ditch, on which some form of tower or fortified house was usually built, often with a palisade around its base, and an outer yard (bailey) enclosed by a palisade and ditch. The bailey was usually large enough to enclose several buildings and animals if necessary. Sometimes there was more than one bailey. In our period the defenses were almost invariably of wood. The main strength of these castles was their earthworks and ditches with their steep banks: the wooden fortifications alone would not have presented a serious obstacle, but the whole structure was very difficult to assault, although the wood was obviously vulnerable to fire in the right conditions. In addition, the castles were relatively cheap and easy to build and did not require a skilled labor force. However, medieval accounts suggesting that mottes could be thrown up in a few days either exaggerate the ease of building or refer to very small mottes. Larger ones may have taken many months to build.

Various reasons have been suggested for the spread of motte-and-bailey castles in the eleventh century: for instance, that they were used widely by the Angevin counts as defense against Vikings, that they arose as a result of “feudalization” (the fragmentation of power and the growth of fiefdoms), and even that the design may have been Viking in origin, hence its widespread use in the territory they were granted, Normandy. Since there is no evidence whatever for such a design in Viking Scandinavia, the last explanation is improbable. Even if correct, the argument that motte-and-bailey castles appeared precisely where fiefdoms did in the feudalization process, in northern Europe, gives a reason for the spread of castles, but not the appearance of a new type of castle. According to D.J. Cathcart King, the earliest known example of the motte-and-bailey design was at Les Rues-des-Vignes (medieval Vinchy), Nord-Pas-de-Calais, known of from 979. Fulk Nerra and Geoffrey Martel, who reigned as counts of Anjou 987–1040 and 1040–1060, used various types of fortification, as often to secure control of territory they had gained as much as to defend their frontiers against Vikings and neighboring lords. They constructed stone towers as well as ringforts and mottes. The deciding factor was probably the speed at which they had to be constructed. The strategy of constructing forts rapidly after an initial advance into enemy territory and then improving them later was used by the Normans in England. Nevertheless, on the continent the simple ringfort continued in use, although some were converted with the addition of a motte. During the Norman conquest of England it seems that ringworks were often built first and converted to motte-and-bailey castles later.

Bernard Bachrach has highlighted Fulk Nerra’s strategy of building each castle no more than 35 kilometers from the nearest—in other words, within a day’s ride. In England and Wales this strategy was particularly useful to Duke William for securing control of a hostile territory. Each motte-and-bailey castle built by the Normans after their invasion was designed so that a small number of occupants could control the immediate district or estate and be safe from attack, but were also within reach of relief from neighboring castles. In addition, the appearance of the castle would have had a powerful intimidating effect on the English. An interesting aspect of William’s castle-building is that most of the sites were new, and in many regions such as Somerset it seems that the old Anglo-Saxon burhs were initially avoided. The most likely reason is the Norman perception of them as centers of resistance, where large concentrations of hostile people were available to attack any garrison. This was not unreasonable, as the fate of the garrison at York in 1069 showed, although there the English had Danish help. The break-up of old estates and the creation of new ones also meant that central locations for control of estates changed, to places where castles were needed by the new landowners.

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