Nearly opposite the cemetery of Callixtus, on the Appian Way, is that of Prætextatus. One of the entrances, situated in the Vigna Molinari, is represented in Fig. 2. A well-worn stairway, trodden by the feet of pious generations, leads to subterranean galleries of considerable extent. It is celebrated as the scene of the martyrdom of St. Sixtus and his deacons, A. D. 259; and as the burial-place of two of them, Felicitas and Agapetus, commemorative epitaphs of whom have been found. Their tomb, accidentally discovered by some labourers in 1857, presents the unique example of a large square crypt, not hewn out of the rock but built of solid masonry, and formerly lined with marble. This is explained by the ancient record that the Christian matron Marmenia constructed their tomb immediately beneath her own house. A Damasine epitaph of Januarius, who suffered under Aurelius, A. D. 162, has also been found here. In this cemetery, too, occurs that _suite_ of chambers, with a hexagonal apartment, known as the chapel with two 184 halls, represented in section and perspective in Figs. 10 and 11. Especial interest attaches to the Catacomb of St. Sebastian from the fact of its being the only one of which any knowledge was retained during the darkness of the Middle Ages. During that obscure period it was known in all the ancient documents as the _Coemeterium ad catacumbas_, and has given their generic name to this vast system of subterranean sepulchres. Lying beneath the property of the Augustinian monks, it enjoyed religious protection in the rudest ages, and was open to the occasional pilgrims to the sacred places of the Eternal City. It is also that which is most frequently visited by modern travellers, being accessible without the special permission which must be obtained for exploring the other Catacombs. It is situated on the Appian Way, about two miles from the Sebastian gate. A stately basilica was erected over the entrance to the Catacomb, it is said in the time of Constantine. A part of the original building which yet remains is claimed to be still older, dating from the first century. With this possible exception, few traces of the ancient structure now exist, the present building having been erected in 1611 by Cardinal Scipio Borghese. The church is very rich in paintings, sculptures, and relics, among which are the reputed head of Callixtus, arm of St. Andrew, and body of St. Sebastian, the impressions of the Saviour’s feet in the stone from the Appian Way, and the very chair in which St. Stephen received the crown of martyrdom, and which was sprinkled with his blood!