Dresden, the capital of the state of Saxony, is located along the Elbe river in the former East Germany. It is a major tourist attraction due to its baroque and rococo historic centre, one of the most beautiful ones in Germany. The city's origins can be traced back to the 13th century when Dietrich, Margrave of Meissen, chose Dresden as his residence. Later Dresden became the capital and royal residence of the Electors and Kings of Saxony, who over the centuries added impressive buildings to the city. Most of the most significant palaces and churches of Dresden date back to the 18th century. Due to its impressive architecture Dresden was called the Florence of the Elbe. The entire historic centre of Dresden was almost completely destroyed by a controversial Allied aerial bombing in 1945. Most of what is visible today has been reconstructed after the war and the reconstruction effort is still continuing. Some of the historic buildings were replaced by modern buildings ("socialist realism" architecture) in the post-war period. The historic centre of Dresden together with the Elbe valley has been a UNESCO world heritage site since 2004.