ansmitted its classic denomination to the church
of S. Salvatore in AErario.

In drawing sheet no. xxix. of my archaeological map of Rome, which
represents the region of the Sacra Via, I have had as much to do with
Christian edifices as with pagan ruins.[92]

VI. MEMORIALS OF HISTORICAL EVENTS. The first commemorative chapel
erected in Rome is perhaps contemporary with the Arch of Constantine,
and refers to the same event, the victory gained by the first
Christian emperor over Maxentius in the plain of the Tiber, near Torre
di Quinto.

[Illustration: Statue of Constantine the Great.]

The existence of this chapel, called the _Oratorium Sanctae Crucis_
("the oratory of the holy cross"), is frequently alluded to in early
church documents. The name must have originated from a monumental
cross erected on the battlefield, in memory of Constantine's vision
of the "sign of Christ" (the monogram [Symbol: Christ]). In the
procession which took place on S. Mark's day, from the church of S.
Lorenzo in Lucina to S. Peter's, through the Via Flaminia and across
the Ponte Milvio, the first halt was made at S. Valentine's,[93] the
second at the chapel of the Holy Cross. The "Liber Pontificalis," in
the Life of Leo III. (795-816), speaks of this strange ceremony. It
was called the "great litany," and occurred on the twenty-third of
April, the day on which the Romans used to celebrate the Robigalia.
The Christian litany and the pagan ceremony had the same purpose, that
of securing the blessing of Heaven upon the fields, and averting from
them the pernicious effects of late spring frosts. The rites were
nearly the same, the principal one being a procession which left Rome
by the Porta Flaminia, and passed across the Ponte Milvio to a
suburban sanctuary. The end of the pagan pilgrimage was a temple of
the god Robigus or the goddess Robigo, situated at the fifth milestone
of the Via Claudia; that of the Christian the monumental cross near
the same road, and ultimately the basilica of S. Peter's. In course of
time the oratory and cross lost their genuine meaning; they were
thought to mark the spot on which the miraculous vision had appeared
to Constantine on the eve of battle. This was not the case, however,
because Eusebius, to whom the emperor himself described the event,
says that the luminous sign appeared to him before the commencement of
military operations, which means before he crossed the Alps and took
possession of Susa, Tur