page_title: Stone Bridge (Regensburg)
section_title: Construction and modifications
hierarchical_section_title: Stone Bridge (Regensburg) / History / Construction and modifications
caption_attribution_description: Deutsch: Regensburger Stadttor an der Donau mitsamt Salzstadel und Hohem Dom St. Peter im Hintergrund
context_page_description: The Stone Bridge in Regensburg, Germany, is a 12th-century bridge across the Danube linking the Old Town with Stadtamhof. For more than 800 years, until the 1930s, it was the city's only bridge across the river. It is a masterwork of medieval construction and an emblem of the city.
context_section_description: The Stone Bridge is an arch bridge with 16 arches. At the south end, the first arch and first pier were incorporated into the Regensburg Salt Store when it was built in 1616–20, but remain in place under the approach road to the bridge. An archaeological investigation was performed in 2009, and revealed fire damage during the Middle Ages. The bridge was originally 336 metres (1,102 ft) long; the building in of the first pier reduced it to 308.7 metres (1,013 ft). The southern, Old Town end of the bridge is half a metre lower than the northern, Stadtamhof end, and the bridge bends slightly because of the course of the river at that point.
  Construction of the bridge was made easier by an unusually hot, dry summer in 1135, which caused very low water levels in the Danube. Some of the bridge piers are on the two islands in the Danube within the city, the Upper and Lower Wöhrd. The others rest on foundations of oak logs on the riverbed, which were constructed inside cofferdams of oak planking. To protect them from being undermined by the river, they are surrounded by pillar-shaped artificial islands or abutments; these were enlarged in 1687. The bridge abutments are a substantial impediment to the flow of water, with as little as 4 metres between them, creating strong whirling currents under the bridge and downstream, which are referred to as the "Regensburg Danube Strudel". Five of them were reduced in size in 1848 as part of construction of the Ludwig Canal, and they were all reduced and strengthened with concrete and stone during renovation work in 1951–62. The construction using abutments is a modification of the technique used by the Romans for the bridge over the Mosel at Trier, where the piers rest directly on the riverbed.
  Watermills were built at the south end of the bridge, making use of the currents it created; the revenues contributed to the upkeep of the bridge. The Bavarians had them burnt in 1633 during the Thirty Years' War; some were rebuilt in 1655 but in 1784 an ice dam on the river destroyed them. One was rebuilt at the foot of the Salt Store for a few more years.
  In the Thirty Years' War, during the Swedish attack on the city in 1633, the fourth bridge span (the third now visible) was blown up. The gap was filled by a wooden drawbridge and only repaired in 1790/91 after it became apparent that the missing section was weakening the bridge.
  The bridge originally had three towers, of which only the south tower, a gate tower to the Old City, survives. The original south tower was built around 1300; beside it stood a chapel of St Margaret. In the mid-16th century this was converted into a debtors' prison and the tower became known as the Debt Tower (Schuldturm). The middle tower was built around 1200. Both the south and the middle towers were destroyed by fire in the Thirty Years' War, when the city was under occupation by the Swedes. They were rebuilt in 1648, the clock being added to the south tower at that time, but the middle tower was demolished in 1784 after being almost destroyed by the ice dam. The north tower (the Black Tower), was probably built in the second half of the 12th century, in association with the bridge itself. It was heavily fortified between 1383 and 1429, including a drawbridge. This tower was damaged in 1809 during the Napoleonic Wars when the French and Bavarians retook the city from the Austrians, and had to be demolished the next year. In 1824/25 the site where it had stood was widened to accommodate a bazaar.
  The chapel was removed and replaced by a tollhouse in 1829. In the early 20th century, when the tramway was built, all buildings between the remaining tower and the Amberg Salt Store were removed, widening the street approaching the bridge, and a wide arch was built over it beside the tower. Late in the Second World War, on 23 April 1945, German troops dynamited the second pier of the bridge immediately in front of that point, and also the eleventh, to slow the advance of American troops. The Americans installed temporary planking the following winter, but the damage was not 
caption: The remaining tower at the south end of the bridge, with tramway arch to the right, and Salt Store; Regensburg Cathedral in the background.
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