The Catacomb(s) of Callixtus is one of the Catacombs of Rome on the Appian Way, most notable for containing the Crypt of the Popes, which once contained the tombs of several popes from the 2nd to 4th centuries.
The Catacomb is believed to have been created by future Pope Callixtus I, then a deacon of Rome, under the direction of Pope Zephyrinus, enlarging pre-existing early Christian hypogea. Callixtus himself was entombed in the Catacomb of Calepodius on the Aurelian Way. The crypt fell into disuse and decay as the relics it contained were translated from the catacombs to the various churches of Rome; the final wave of translations from the crypt occurred under Pope Sergius II in the 9th century, primarily to San Silvestro in Capite, which unlike the Catacomb was within the Aurelian Walls. The Catacomb and Crypt were rediscovered in 1854.
The underground cemetery includes several areas. The area of the Popes is the most important and venerated crypt of the cemetery, called 'the little Vatican' as it was the official burial place of nine popes and, probably, of eight dignitaries of Rome's 3rd century Church. In the walls you can still see the original inscriptions, in Greek, of five popes. On four tombstones, near the name of the pope, there is the title of 'bishop', since the Pope was regarded as the head of the Church of Rome, and on two of them there is the Greek abbreviation of MPT for 'Martyr'.
Passing through imposing galleries full of loculi, we reach five small chambers, truly family tombs, commonly known as the cubicles of the Sacraments, and particularly important for their frescoes.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.