The only significant exception is the great archway opened in the facade wall in the 11th century and used by the Crusaders as the access between the rotunda and their abutting church. Inside the rotunda, the fourth century remains are numerous, including the rectilinear facade-wall, the two lateral vestibules, the great outside periphery wall, circular on the interior, polygonal on the outside, together with its niches forming small apses, and the emplacement of the support points of the interior arrangement of the entire building; all these still existing features are the original ones. It is a rarity to find such an early Christian monument so relatively well and abundantly preserved.