Basilica of Saint Lawrence outside the Walls

What is there today

The church you walk into is two buildings joined end to end, not quite on the same axis (it.wikipedia; Turismo Roma). The nave from the door is the 13th-century church of Pope Honorius III; at its far end two flights of steps climb to a raised choir, and that choir is the 6th-century church (it.wikipedia; de.wikipedia).

• Pelagius II’s church (579–590). A three-aisled hall about 32 m long and 21 m wide, with five columns a side and an upper gallery above the aisles (the operator; Turismo Roma), almost 20 m high (de.wikipedia). Every column and capital in it is reused from older buildings; the two capitals carved with arms and Victories at the western end of its nave are dated to the 3rd century (the operator). Pelagius dug the church into the hillside of the catacomb so that its sanctuary lay directly over the martyr’s grave (de.wikipedia).
• The mosaic on the arch. The arch that once opened into Pelagius’s apse keeps its late 6th-century mosaic: Christ seated on a globe between Peter, Lawrence and Pelagius II, who holds out a model of his church, on one side, and Paul, Stephen and Hippolytus on the other (the operator; Turismo Roma), with Bethlehem and Jerusalem in the corners (de.wikipedia).
• The tomb of Lawrence. Below the choir, the confessio holds the tombs of Lawrence and of Stephen, the first martyr (it.wikipedia; en.wikipedia). The four small columns of green marble just past its stairs are held by tradition to come from the first monument Constantine raised over the grave, and a reused inscribed slab of the 5th or 6th century stands at its entrance (the operator).
• Ancient stone in the later church. The 22 columns of the 13th-century nave, all different, may come from Constantine’s basilica (it.wikipedia; Turismo Roma), and so, probably, do the six reused columns of the portico outside (the operator). Inside the front wall, Cardinal Guglielmo Fieschi, who died in 1256, lies in a 3rd-century sarcophagus carved with a wedding scene (en.wikipedia; it.wikipedia), and the portico holds an ancient sarcophagus carved with putti picking grapes (en.wikipedia; Turismo Roma).

The catacomb. Lawrence was buried in the catacomb of Cyriaca, named after the woman whose land it was dug in (en.wikipedia; it.wikipedia). You go down into it from the cloister, and three entrances in the basilica reach it (it.wikipedia). Published counts give it four or five levels (it.wikipedia; the operator), and the operator says the top two were obliterated by the churches built over them. It is poorly preserved - pilgrims and relic hunters never stopped visiting it, and the Second World War bombing and the building of the Verano cemetery did the rest - and only a limited stretch can be visited (it.wikipedia). The shrine of two other martyrs, Abundius and Herennius, was found in it in 1947–1949 (it.wikipedia; en.wikipedia).

The cloister, built in the 12th or 13th century (it.wikipedia; the operator), displays Christian and pagan sarcophagi, 3rd-century sarcophagi carved with wavy fluting, and inscriptions from the catacomb and the cemetery above it, among them a marble inscription recording work done by Pope Damasus (366–384) (the operator).

What you will not see is Constantine’s own church. It was a large basilica with an aisle that curved round its apse, about 99 m long and 35 m wide, some 30 m south of the present church under what is now the Verano cemetery (de.wikipedia; the operator); it had probably fallen into ruin by the 12th century, and excavation found only a few remains (de.wikipedia).