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:Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.