Over the entrance _outside_ is a relief of Christ giving the keys to
Peter; _inside_ the vestibule is Giotto's (1298) celebrated mosaic,
representing our Lord sustaining Peter when he was about to sink
whilst walking on the sea. Opposite are the great bronze doors, opened
only on special occasions, the work of Antonio Filareto and Simone
Donatello in the fifteenth century. The upper panels represent in
relief our Saviour and the Virgin, below whom are SS. Peter and Paul;
Peter is giving the keys to Pope Eugenius IV. Beneath are the
martyrdoms of Peter and Paul: in the former is represented the
pyramidal tomb which stood in the Borgo Nuovo, and which was destroyed
by Alexander VI. The smaller reliefs represent scenes from the life of
the Emperor Sigismund--his coronation, the council of Florence, and
his entry into Rome. The framework represents satyrs, nymphs, fauns,
Leda and the Swan, Ganymede, the Fox and the Stork, with reliefs of
fruit and flowers, and medallions of Roman emperors. The walled-up
side door, on the right, is the Porta Santa, which was formerly opened
on Christmas-eve of the years of jubilee--every twenty-fifth year.
_The first_ inscription relates the gift of olive-yards to provide oil
for the lamps given by Gregory II.
_The second_, the Bull of Boniface VIII., of the indulgence granted at
jubilee.
_The third_, Panegyric of Charlemagne on Pope Adrian I.