LOS ANGELES, CA (Catholic Online) - This ancient church was transformed over the centuries from a private home and site of clandestine Christian worship in the first century to a grand public basilica by the 6th century, reflecting the emerging Roman Catholic Church's growing acceptance and influence.

In the late 1st century AD, an apartment building and mansion were built here, separated by a narrow Roman street. These were built on top of earlier structures that were destroyed in the great fire of 64 AD under Nero.

A Christian community is believed to have gathered in the mansion by the 2nd century. The community was known as the titulus Clementis, probably named for the owner of the mansion.

Some years later, a large hall was built over the inner courtyard and ground floor rooms of the adjoining mansion. It may have been built with the express purpose of housing the Christian community.

Not long after Christian persecution ended under Constantine in 313 AD and Christianity became the official religion of the empire in the 380s AD, the hall became a full-fledged church. This is the lower church that can still be visited today.

The main, upper church of San Clemente is one of the most richly decorated churches in Rome. The vast majority of its architecture and art dates from its construction in the early 12th century.

The most striking sight is the 12th-century apse mosaic, in a golden-bronze color and featuring a large crucifix in the center. Growing from and around the crucifix are vines, associating the cross with the Tree of Life.

In the center of the apse is a throne, whose back is part of a martyr's tomb. Under a baldacchino, the high altar contains the relics of St. Clement of Rome and St. Ignatius of Antioch.