Plan of the place called Platonia at St. Sebastian, outside the walls of Rome. This place, much decorated by the piety Pope St. Damasius, in the fourth century, is partly subterranean, and placed on the left of the choir of the church, between it and the cemetery of St. Caliztus, pope and martyr. "Nobilissimum," according to the expression of d'Aringhi, "quod caeteris tum amplitudine, tum antiquitate praestat." There are also three niches, which have probably been tombs, excavated in the tufo, and lined with brick, a marble bench is placed all around. In the center of this place was the episcopal or pontifical seat, and the walls were lined with marble, from which arose the title of Platonia. St. Damasius, who cultivated the sacred muses, engraved on the marble: HIC HABITASSE PRIVS SANSTOS COGNOSCERE DEBES NOMINE QVISQVE PETRI PARTITER PAVLIQVE REQVIRIS . This is the entrance to the Catacombs of St. Sebastian.