The heart of the ancient imperial city is the cathedral which was the first German building to be declared a World Heritage Site of the UNESCO. The oldest part is the octagonal central building, which was built around 800 under Charlemagne. In the palace chapel more than 30 German kings were crowned. Under the dome there is the marble throne of Charlemagne and a chandelier, which was donated by Frederick Barbarossa. Because of the rich tradition and the close border to Belgium and the Netherlands, Aachen is known as a European city in which many cross-border initiatives were started.