Regensburg (also Ratisbon, Latin Ratisbona) is a city in Bavaria, located at the confluence of the Danube and Regen rivers, at the northernmost bend in the Danube. The Celtic name Radasbona was the oldest name given to a settlement near the present city. This medieval town contains many buildings of exceptional quality that testify to its history as a trading centre and to its influence on the region as of the 9th century. It has preserved a notable number of historic structures spanning some two millennia, including ancient Roman, Romanesque and Gothic buildings. Regensburg's 11th - 13th -century architecture - including the market, City Hall and Cathedral, still defines the character of the town marked by tall buildings, dark, narrow lanes, and strong fortifications. The buildings include medieval Patrician houses and towers, a large number of churches and monastic ensembles as well as the Old Bridge, which dates from the 12th century. The town is also remarkable for the vestiges that testify to its rich institutional and religious history as one of the centres of the Holy Roman Empire that turned to Protestantism. Regensburg had little damage from Allied air raids during World War II and thus has an almost intact medieval city center, which has been listed in 2006 as a UNESCO World Heritage Site.