Crypt in Basilica at Boulogne-sur-Mer. Source Ville de Boulogne-sur-Mer/VAH

The Crypt at Boulogne-sur-Mer

The Basilica at Boulogne-sur-Mer was built in the 19th century on top of a medieval church. Beneath is one of the largest crypts in Europe. After years of archaeological excavations and restoration it shines once more.

Crypt in Boulogne-sur-Mer Source: Inrap/Dominique Bossut
Crypt in Boulogne-sur-Mer Source: Inrap/Dominique Bossut

For several years archaeologists have been excavating in the vast crypt beneath the basilica in Boulogne-sur-Mer in Northern France in the department of Pas-de-Calais.

The history behind is the rediscovery of the Romanesque crypt in 1827, when the construction of the present church began on top of the ruins of the medieval basilica. This had probably been filled The foundation of this may perhaps be dated to the 7th century.

The city has Roman roots and was originally called Gesoriacum. It has sometimes been conflated with Caesar’s Portus Itius. However, from AD 43, when Claudius invaded England it formed the major port connecting the Roman Empire to Britain. Until 286 it was the chief base of the Roman Britanninc fleet. At some point the name of the city changed to Bononia. At the end of the 4th century, Zosimus called it Germanorum or “German-speaking” signalling its role as stepping-stone for the Anglo-Saxon mercenaries, who were the initial bridgehead of the later immigration of Germanic-speaking people into England.

Since the 1970’s extensive archaeological excavations have succeeded in locating the Roman military camp, which covered about 12 hectares. The medieval walls of the city from the 13th century still mark this area.

The present Basilica is located in the corner, where the ancient barracks were situated. Built in the first half of the 2nd century, they were in constant use until AD 260. During excavations in the crypt a piece of Roman road, probably one of the internal streets in the camp, has been found. Another find seems to be the remains of the earlier camp erected by Claudius.

Another result of the excavations have been the location of part of a medieval cemetery and an ossuary of bones from the 14th to 15th centuries enabling a study of where people living in the city at that time came from and their general health.

Crypt Reopened

Reliquary of the Holy Blood from 1308 Treasury of Basilica of Boulogne-sur-mer
Reliquary of the Holy Blood from 1308. Source: Treasury of Basilica of Boulogne-sur-mer

In June 2015 the crypt reopened showing off its spectacular medieval murals as well as a new museum presenting the treasury of the Cathedral: sculptures, reliquaries etc. One of the more prominent pieces is a reliquary of the Holy Blood from the 14th century, which has been attributed to Guillaume Julien, the Goldsmith of Philippe IV (Phillippe de Bel) at the occasion of the marriage between his daughter, Isabelle de France, with Edward II of England, celebrated at Boulogne-sur-Mer in 1308. It measures 7.5 cm in diameter and is made with cloisonné enamel, pierced by an oculus through which the holy blood might have been glimpsed.


La Crypte. 2000 ans d’histoire


Boulogne-sur-Mer: de la Classis Britannica aux Temps modernes.


Du culte des reliques à celui du Précieaux Sang. (From the worship of Relics to the Cult of Precious Blood)
By Andé Vauchez.
In: Tabularia “Études”, No. 8, 2008 – p. 81 – 88.