At the west end of this aisle, over the stairs, are the remains of a
painting of the Crucifixion of S. Peter; and in the right-hand
corner, S. Cyril's parting audience with Michael III. In the opposite
corner is a baptism of some barbarian by S. Cyril, beyond which the
projecting brickwork marks the site of the tomb of S. Cyril.
The nave is formed by a line of seven columns in their original
places, in a wall of _débris_ built to support the church above. These
columns are of beautiful marbles, and stand upon a wall of the
imperial period, which has been traced for 98 feet.
At the west end of the north aisle a flight of narrow steps leads down
to a passage, 25 inches wide, formed between massive walls: that on
the right is brick of the imperial period, forming the wall of S.
Clement's house; that on the left, tufa, of the kingly period, being
part of the walls of Servius Tullius. This has been heightened by a
travertine wall of the republican period. The tufa wall has been
traced for 500 feet, and the travertine wall upon it for 410 feet.
About 20 feet is still buried, showing how low ancient Rome was in
this valley. At the end of this passage another flight of steps leads
up into the south aisle. In the centre of the passage is an entrance
through the imperial wall (now blocked up on account of the water)
into