and San
Lorenzo fuori le Mura, were enlarged in a westward direction, so that
the positions of the altar and entrance were reversed; and, in several
of the early basilicas at Rome, a space near the entrance of the nave
was screened off, from which penitents and catechumens might watch the
service. But, in the first instance, the eastern chancel and the
structural _narthex_ appear to have been introduced from the eastern
empire. Neither at Ravenna nor at Rome did bell-towers originally form
part of the plan of the basilica: the round _campanili_ of both churches
at Ravenna are certainly later additions. It may also be noted (1) that
ordinarily the aisles were single, not double as at old St Peter's. (2)
The columned screen of the apse at old St Peter's appears to have been
exceptional. The ordinary screen or _cancelli_, from which is derived
our word "chancel" for the space thus enclosed, was a low wall. This is
the arrangement at the basilica of San Clemente, in which the enclosed
quire also remains. (3) The transept, even in Rome, was an exceptional
arrangement, and does not appear in the basilicas of Ravenna.

Sec. 6. Another type of plan, however, was used in Rome for churches
devoted to the special purposes of burial and baptism. In this case the
buildings were planned round a central point, and at Rome were uniformly
circular. Recesses round the walls of the mausoleum-church contained
sarcophagi: in the centre of the baptistery was the great font. The
church of Santa Costanza, outside the north-eastern walls of Rome,
circular in plan, with a vaulted aisle surrounding the central space,
was built by Constantine the Great as a tomb-church for his family, and
was also used as a baptistery. Both these uses were direct adaptations
of pagan customs. The baptistery, with its central font for total
immersion, was simply a large bath-room, like the great rotunda of the
baths of Caracalla. The mausoleum preserved the form of which the finest
example is the tomb of Hadrian, now known as the castle of Sant' Angelo.
In the course of the middle ages, certain tomb-churches in Rome, with a
centralised plan, were turned into places of public worship. But, for
the plan of the ordinary church, the basilica, with its longitudinal
axis, was general. In the eastern empire, on the other hand, the
centralised plan was employed from an early date for large churches; and
in this way was evolved the magnificent style of architecture which
c