Its precise function is not known but it is the most romantic and also the most enigmatic monument in Nîmes—doubtless linked with the imperial sanctuary.
The lateral passages used to lead to an upper level but the various vaults and the niches in the large room do not match the components of Greco-Roman temples. The origin of its name is also a mystery.
During his stay in Nîmes around 1570, the Venetian architect Palladio made numerous sketches of the building before a fire gave it its present appearance. Today, it consists only of a barrel-vaulted nave and two lateral passages, one of which (the south-east one) was almost totally destroyed.