This road leads from the old Porta Navalis in the Trastevere, the city “across the Tiber,” direct to Portus the port of Rome, a construction of Claudius when Ostia (Centumcellæ) was unable to cope with the commerce of the capital. Three cemeteries, according to the ancient Itineraries, were excavated on the Via Portuensis. That of Pontianus, the best known of the three, where lie the remains of SS. Abdon and Sennen; and a second, nearly five miles from the city, the Catacomb of Generosa. There is a third, the Cemetery of S. Felix, the position of which has not yet been discovered. _The Cemetery of Pontianus._--Pontianus was a wealthy Christian of the Trastevere quarter, who used in the second century--probably in the latter years of the century--to gather his fellow-Christians to prayer and teaching in his house. The cemetery which bears his name was originally excavated in one of his gardens. The old Pilgrim Itineraries speak of there being a vast number of martyrs in this Catacomb--“innumerabilis multitudo Martyrum.” Several of these are named; the most notable, however, are the two noble Persians, Abdon and Sennen, who, visiting Rome at the time of the persecution of Decius, suffered for their faith. In this Catacomb there is a well-known ancient baptistery of considerable size, which was richly decorated in the sixth century. Such baptisteries have been found in other Catacombs, notably in that of S. Priscilla, a very ancient and vast cemetery which will be described with some detail later. The remains of the more famous martyrs were removed into the city at the period of the great translation of sacred bodies in the ninth century, after which date this cemetery ceased to be visited. It has only been partially explored. _The Cemetery of S. Felix_ mentioned in the Itineraries is completely unknown as yet. _The Cemetery of Generosa_, on the road to Porta, is not alluded to in the Pilgrim Guides, no doubt owing to its distance--some five miles--from the city. Lanciani gives a vivid description of its story and of its discovery in 1867. It is of small extent, and apparently was excavated in the persecution of Diocletian, _circa_ A.D. 303, in what was once a sacred grove belonging to the College of the Arval Brothers, but which had been abandoned, probably after the dissolution of the Brotherhood, which is supposed to have taken place about the middle of the third century. IV THE VIA OSTIENSIS The _Via Ostiensis_, on the city side of the Tiber, one of the principal roads of the Empire, begins at the ancient Porta Ostiensis, known from the sixth century onwards as the Porta S. Pauli, and leads to the old harbour of Ostia. The Pilgrim Itineraries enumerate three cemeteries as situated hard by this road--the tomb of the Apostle S. Paul with the little Cemetery of Lucina, the Cemetery of Commodilla, and that of S. Theckla.