Basilica di Sant'Agnese fuori le Mura & Chiesa di Santa Costanza

Lonely Planet review

The apse of the 4th-century Basilica di Sant'Agnese fuori le Mura, built by Constantine, has a 7th-century mosaic depicting St Agnes standing on flames. According to tradition, the 13-year-old Agnes was burnt at the stake by the Emperor Domitian but remained miraculously unharmed. Unfortunately, she was beheaded on the spot where the Chiesa di Sant'Agnese in Agone now stands in Piazza Navona and buried in the catacombs beneath this church.

In the same complex, across the convent courtyard, is the Chiesa di Santa Costanza. Built as a mausoleum for Constantine's daughters, Constance and Helen, the pretty circular building has a dome supported by 12 pairs of granite columns. The covered walkway outside of the arches has a barrel-vaulted ceiling that is covered with beautiful 4th-century mosaics, said by some to be the world's oldest Christian mosaics. There were once mosaics in the dome but they were destroyed by Paul V in 1622.