Rome is built on a crust of history. It seems that wherever they break through, a secret museum is found lying beneath the ground. Currently, some 400 excavations are accessible, varying in degree of difficulty presented by the site and in terms of the amount of red tape required to arrange a visit.
One which requires no forward planning, but offers an easy walk through a four-layer cross section of Roman history, is the medieval Church of St Clemente. Simply descend a staircase in the nave to arrive in an earlier Basilica, larger than the one above it, built around 375 AD.
Both churches are richly decorated, the 12th century church with mosaics, the earlier one with frescoes. Sacked by the Normans, it became the foundation for the present church and lay forgotten until 1827 when a determined priest started the 40-year excavation project that brought it to light.
Down a further level is one of the best preserved shrines to Mithras yet found under Rome. This Persian religion, popular with the Imperial soldiers, had more followers than Christ at the beginning of the 4th century. The religion involved the sacrifice of a bull, and in the floor is the channel down which the blood of the animals ran. There are rooms with stuccoed ceilings, the dining room with stone benches, and what is thought to have been a schoolroom for young initiates.
Finally, under this pagan temple, you visit the still unexcavated foundations of the Roman buildings burned in Nero’s great fire and walk the cobbles of a 1,900-year-old Roman street, now 30 feet underground. The Church of San Clemente is at Via San Giovanni in Laterno, open every day from 9.00 a.m. to 12.30 p.m. and from 3.30 p.m. to 6.30 p.m.