St. Gereon's Basilica, Cologne

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 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 was probably a mausoleum of a rich and powerful early Christian family in the provincial capital of Germania Inferior in the time of Emperor Constantius II.

In the years 1060 to 1062, under Archbishop Anno II, a new, elongated choir room was added for the members of the monastery, noble canons, and a crypt was set up underneath.

In the years 1219–1227, the early Christian oval building adjacent to the west was reinforced and encased on the outside, transformed into a decagon and at the same time raised with Gothic galleries and covered with a central dome.

St. Gereon has a highly irregular plan, the nave being covered by a decagonal oval dome, 21.0 m long and 16.9 m wide, completed in 1227 on the remains of the antique central building.

The decagon and eastern apse were equipped with color window cycles by Georg Meistermann and Wilhelm Buschulte.

It contains 190 parchment pages of mass prayers and a pre-stapled calendar in which the feast of Saint Gereon on October 17th and the church consecration on July 28th are mentioned.

The London piece of border from the tapestry depicts a lion's-head mask, while other surviving fragments (in the Germanisches Nationalmuseum, Nuremberg, and the Musee des Tissus, Lyon) show a design of roundels containing griffins attacking bullocks.

This motive was possibly based on an eighth century Byzantine silk found in a tomb in the Basilica of St. Ursula, Cologne.