St. Gereon's Basilica

Later medieval structure with Roman building fabric largest occidental dome between Hagia Sophia and Florence Cathedral.

St. Gereon's Basilica is a basilica church in Cologne, Germany, dedicated to Saint Gereon. Begun in 1067, it is one of twelve great basilicas in Cologne that were built in the Romanesque style. St. Gereon features the largest dome built in the West between the erection of the Hagia Sophia in the sixth century and the Duomo of Florence in the fifteenth. The oval dome, being 21.0 m long and 16.9 m wide, was completed in 1227 on the remains of Roman walls, which are still visible. The dome is also notable for its rare decagonal structure.