LOS ANGELES, CA (Catholic Online) - Earlier accounts also report that Constantine built a baptistery on the site, in which both Constantia and Constantine's sister were baptized by Pope Sylvester. It was long assumed that the existing mausoleum is this baptistery, but excavations beneath its north end in 1992 revealed a triconch, or clover-shaped building that is a more likely candidate.

It was long thought that Constantia was buried in the mausoleum, but new data indicates the building was probably still unfinished at that time, so she was probably buried either in the baptistery or in the apse of the funerary hall.

The chief highlight of Santa Costanza is the barrel vaulting of the ambulatory, which is covered in original 4th-century mosaics. These mosaics display a fascinating mix of pagan and Christian symbolism and imagery.

According to the scholar G. Mackie, Santa Costanza's art reflects "the emerging iconography of the Christian faith in its first years of legitimacy in the Roman Empire."

The Rough Guide to Italy similarly comments that Santa Costanza "perhaps more than any other building in Rome illustrates the transition from the pagan to Christian city in its decorative and architectural features."

Dating from the 360s or 370s, the ambulatory mosaics were designed in corresponding pairs leading towards the niche with the sarcophagus, where the flanking mosaic pair is the most elaborate. The pair by the entrance is a simple, geometric design; this is following by a pair with a circular motif with animals and figures. Next are scenes of grape harvesting, then roundels with a leaf design, busts and figures. The pair by the sarcophagus has branches, amphorae and peacocks. The imagery is capable of both pagan and Christian interpretation, which is representative of Constantine's religious policy.