06 February 2024

The Ancient Peninsula of Regensburg


It is a generally accepted view among local historians in Regensburg that the city's islands were formed from an extremely long and extremely narrow peninsula by the catastrophic flood of 1304. This serpentine stretch of land stretched from the mouth of the Naab to Regensburg, i.e. the estuary of the Naab ran parallel to the Danube for about six kilometres. There are, however, some aspects that may call into question the existence of this rare hydrological phenomenon.


I first came across the above illustration on the inside cover of the publication "Regensburg zur Römerzeit", which depicted the hydrological situation shown in the above picture as a fact. According to a brief description of the landscape, the Naab did not flow into the Danube at Mariaort in Roman times, but ran parallel to the Danube for almost six kilometres, passing Kneiting, Winzer, Steinweg and Stadamhof, taking the Regen river on the left bank and flowing into the Danube somewhere at the lower tip of the present-day Unterer Wöhrd, east of Regensburg. In other words, when the second stone bridge was built on the Danube between 1135 and 1146, the famous Steinerne Brücke was still arching over this peninsula to the north bank. The huge peninsula was carved up into four separate islands (Mariaorter Wöhrd, Winzer Wöhrd, and in Regensburg the Lower and Upper Wöhrd) by the catastrophic flood of 23 May 1304. Local vernacular is calling the Danubian islands Wöhrd, which derives from the Middle German word 'werd', while in northern Germany the more familiar sounding form 'Werder' is used.


The "Regensburg Peninsula" already appear in the work of Otto von Freising, who said that the Naab flowed into the Danube at Regensburg. The local chronicler Eberhard von Regensburg is consistent in his description of the events of 1304:
„Anno Domini 1304. Cum aqua Danubii transiens per pontem Ratisponensem omnio versus litus apuilonare declinasset, et litora prope civitatem sicca et arida reliquisset, ceves Ratisponenses artificiose et mulits laboribus et expensis ipsam aquam, ut iterum prope civitatem flueret, ad loca pristina per strues lignorum et congeries lapidum reduxerunt.”
Early medieval hydrographic conditions were already described by the local historians of Regensburg, Plato-Wild (1710-1777), Gemeiner (1726-1823) and Gumpelzhaimer (1766-1841), whose views were later confirmed by detailed research by Adolf Schmetzer. Karl Bauer, in his monumantal local history book (Regensburg - Kunst, Kultur und Alltagsgeschichte), adds to the above theory that at the time of the construction of the Roman legionary camp Castra Regina (A.D. 180), a change in the riverbed probably caused the Unterer Wöhrd to form a separate island. At Bauer, the date of the flood disaster was two days later, 25 May 1304. On that date, the Danube between Winzer and Pfaffenstein broke through the Regensburg Peninsula and the main riverbed was moved into the old bed of the Naab between the present-day Oberer Wöhrd and Stadtamhof. According to some local oral traditions, the northern branch of the Danube was still called the Naab around 1915.

The section of the Danube between the Naab and the Regen in 1829 (source)

The result was that the free imperial city of Regensburg lost its Danube port, its customs revenue, its mills ran dry, all of which threatened the city's economical power. As the city was in frequent dispute with the town of Stadt am Hof, on the other side of the old Naab, under the jurisdiction of the Bavarian prince-elector, the locals had to act very quickly. It is not clear whether in the same year or in the summer of 1305, during a very dry period when it was possible to cross the shallow Danube, a water control structure called Wöhrloch was built at the top of the Oberer Wöhrd, which was intended to both return most of the Danube's discharge to its original course and leave some (border) water between the Regensburg-owned Oberer Wöhrd and the neighbouring Stadamhof. The Wöhrloch, consisting of a combination lock and weir, was, like the stone bridge, a marvel of engineering on such a grand and rapid scale. However, for centuries it was the source of strife between the city of Regensburg and the Bavarian prince-elector, who wanted to widen the basin to allow larger ships to enter Stadtamhof, boosting trade. Disputes over water management sometimes led to the Wöhrloch being destroyed by the military.

The Wöhrloch in 1638 (source)

In addition to the historical plot, which is worthy of Ken Follett's 'Pillars of the Earth', the question arises: can such an unstable formation be created hydrologically on a river with such a variable flow over such a long period of time? Although the historical sources are clearly "pro-peninsula", there are some hydrological factors that may call into question its existence and its persistence over many centuries.
  • The Danube reaches its most northerly point at Regensburg, where it makes an almost right-angled bend at Winzer, changing from a northeasterly to a southeasterly course. There is also a bend with similar parameters just above the mouth of the Naab, both of which have in common that they head towards a steep hillside. The development of the bend in the river has therefore washed the left bank year after year, and has thinned the peninsula most in the vicinity of Winzer, which is consistent with what historians say about the site of the 1304 breach. 
  • The parameters of the peninsula also suggest that it was not very stable: it was 6 km long from the mouth of the Naab to Regensburg and probably 100 m wide at most. If we take the distance between the Roman castellum of Großprüfening and the hillside above Mariaort, the peninsula was located in a river floodplain cross-section of up to 600 metres in width. In such a section, major floods have had the opportunity to breach the floodplain several times over a period of 1200 years.
  • The only permanent watercourse between the Naab and the Regen is on the left bank, the Brückelgraben. This is a relatively short stream with a low discharge, but it probably built up a cone of sediment in the Danube (or earlier in the Naab bed) from the alluvium carried by the hillside area during major rainfalls, forcing the river of the northern branch southwards, which may ultimately have caused the gradual thinning of the land mass. 
Based on the sources, it seems more likely that the Danube's longest peninsula did exist, but reconstructing exactly how long and how its gradual thinning took place would deserve further research.

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