1One of the unsolved questions of medieval archaeology in Central Germany is the location of the Saxon castle of Hocseburg (Fig. 1), which is mentioned in the Annales Regnis Francorum (Annales, Internet 1). The hypothetical identification of the castle with the site of Seeburg on Lake Süßer See in Saxony-Anhalt (Grimm, 1958; Steuer, 2000, Internet 1), as well as the recently suggested alternative location at the Hünenburg near Watenstedt in Lower Saxony (Internet 2), fail to meet the conditions set down by information from the written sources. A better match is presented by a site rediscovered by aerial reconnaissance on the western side of Lake Seehausen in Saxony-Anhalt. This site has now been investigated, applying geomagnetics, aerial photography and Lidar-data, in an effort to confirm the identification.
Figure 1. The Frankish Empire between 481 and 814 with the Hocseburg castle marked in red. Hocseburg was the stronghold of the Saxon Duke Theoderic in the first half of the 8th century; Charlemagne incorporated the region into his realm in the 770s (modified map from the Historical Atlas by Shepherd, 1911).
2The castle was held by the Saxon Duke Theoderic and played an important role in the armed conflicts between the Carolingians and the Saxons. It was besieged by the armies of Pepin the Short, the son of Charles Martel and father of Charlemagne, in the course of three military campaigns in 743, 744 and 748, prior to Pepin becoming the first Carolingian ruler of the Frankish kingdom in 751. The campaign of 748 was reported in the Annales Mettenses Priores and according to the events presented there, the location of Hocseburg castle should be searched in the vicinity of the river Oker when meeting the Saxon and Frankish armies to do battle.
3The investigated area is situated on the western shore of Lake Seehausen, on Burghügel (castle hill) which slopes down steeply towards the lake. The area of the destroyed castle is now farmland and pastures. Old sketches show a castle with three ring walls encircling an area of 10 ha. The ramparts cannot be seen anymore, having been ploughed under in the 1970s. A caesium-magnetometer survey in November 2018 and January 2019 covered an area of 4.2 ha, investigating the innermost, i.e. first enclosure, and the northern area between the first and second rampart (Fig. 2). The main findings are:
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The castle was built on the site of pre-existing archaeological features, which were cut by the ditches and built over by the walls of the castle.
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There is no evidence of stone buildings.
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A single gate leads through the second wall.
4Satellite images from Google Earth and aerial photographs taken during aerial reconnaissance flights, were used to map ditches outside the surveyed area. Remains of walls were detected and mapped using a high-resolution digital terrain model (Fig. 2). Surprisingly, the southern parts of the second and third ramparts did not reach the shore of the lake, leaving an apparent gap in the defences. The problem of the strategic gap was resolved when, the water level in the lake in the digital terrain model was raised some 9 m. At 140 m a.s.l. the lake took on a sickle-shaped form, providing effective protection for the castle from the south and east. The three ramparts guarded the north-western hinterland.
Figure 2. The fortification on the castle hill on the western shore of Lake Seehausen: three earthen ramparts (light brown) and accompanying outer ditches (green). The present shoreline is at 131.8 m a.s.l. (caesium-magnetometry with Smartmag SM-4G ‘special‘, sensitivity +/- 10pT, duo-Sensor-configuration, two sensors 0.5 m apart in parallel mode, sampling in walking direction ca. 0.1 m, resampling to 0.25 m).
5The results of non-invasive and non-destructive methods, coupled with an analysis of the written sources, have delivered strong arguments in favour of the proposed location.
6According to the sources, the Saxon and Frankish armies faced each other for battle on the river Oker, which the Franks reached after having captured the Saxon castle of Hocseburg. This would situate the castle in the vicinity from the river Oker. The postulated identification with the village of Seeburg fails to meet this condition, being located 120 km from the river.
7The Hocseburg must have been a strongly fortified castle to withstand three Frankish sieges, even if only for a brief time, and to provide sufficient space for the Duke of Saxony Theoderic and his retinue.
8The geophysical survey revealed no stone architecture inside the castle, therefore, it should be dated to before the 10th century when stone was introduced as a building material; according to the written sources, the castle was raised in the first half of the 8th century, a date that might match this finding, but needs to be verified by excavation.
9The castle was built before the Franconian village of Seehausen developed (late 8th/early 9th century) (see below).
10The research also demonstrated that in early medieval times the landscape on the opposite, eastern side of the lake was made up of a low peninsula surrounded by shallow waters (Fig. 3). The first churches and houses were built here sometime after the Frankish conquest in the 770s with the St Laurentius Church in the centre and the old St Paul’s Church further north. To gain more land for village development, the lake level was lowered by removing a natural barrier about 800 m east of the village and channelling the water from the lake through the valley of the Röthebach brook. The lowering of the lake level turned the fortifications ineffective by opening up the southern flank. Only the innermost wall continued to have some defensive value. During Carolingian and Ottonian times the castle served as a stage stop for kings and their retinue travelling along the important road from Magdeburg to Schöningen, a day’s journey from both. The castle was not mentioned in documents for the years 966 (“locus sehusen”) and 1012 (“rex ad Sehusun venit”) mentioning only the village of Seehausen. The same goes for the village named Borchzehusen situated on the so-called Burgberg (castle hill) directly west of the castle, which was mentioned in a document from 1305. This village was abandoned in 1381 at the latest.
Figure 3. The present situation of the town of Seehausen on the east bank and of the castle hill on the west bank of the lake, with the current water level at 131 m a.s.l. The water level in the 8th century was much higher, roughly 140 m a.s.l. (blue line), and was determined probably by a natural barrier removed in early medieval times to channel off the water through the Röthebach valley.