St. Gereon's Basilica, Cologne

St. Gereon's Basilica (Basilika Sankt Gereon) is a German Roman Catholic church in Cologne, dedicated to Saint Gereon, and designated a minor basilica on 25 June 1920.

In the core of St. Gereon, significant remains of an oval central building with nine cones of ancient Roman architecture from the second half of the 4th century (between 350 and 365) have been preserved. This, the lower part of today's decagon, is one of the most important examples of ancient representative architecture north of the Alps and, alongside the somewhat older Trier Cathedral (core building around 340) and the Trier Aula Palatina of Constantine the Great (around 311), which has been used as a church since 1856, is one of the oldest still existing Sacred buildings in Germany.

The first documented mention of a church dedicated to St. Gereon in this location dates back to 612, for which probably only the Roman building was used. Around 800 AD, Archbishop Hildebold had a rectangular choir added to the oval building, into the ancient cavaedium (atrium) around 800 AD and Archbishop Arnold II von Wied added the current choir gallery, apse, and transepts from 1151. The ancient mausoleum was strengthened, sheathed on the outside, converted into a decagon and elevated with Gothic galleries and a central dome between 1219 and 1227. It is one of twelve great churches in Cologne that were built in the Romanesque style.