PORTUS, an ancient harbour of Latium, Italy, on the right bank of the Tiber, at its mouth. For its origin see OSTIA. Claudius constructed the first harbour here, 21 m. north of Ostia, enclosing an area of 17o acres, with two long curving moles pro jecting into the sea, and an artificial island, bearing a lighthouse, in the centre of the space between them; the harbour thus opened directly to the sea on the north-west and communicated with the Tiber by a channel on the south-east. The object was to obtain protection from the prevalent south-west wind, to which the river mouth was exposed. Though Claudius, in the inscription which he caused to be erected in A.D. 46, boasted that he had freed the city of Rome from the danger of inundation, his work was only partially successful. The Via Portuensis m.) ran over the hills as far as the modern Ponte Galera, and then straight across the plain. An older road, the Via Campana, ran along the right bank of the Tiber. In A.D. 103 Trajan constructed an other harbour still well preserved farther inland—a hexagonal basin enclosing an area of 97 acres. It communicated with the harbour of Claudius and with the canal constructed by him (though it bears the name Fossa Trajana) now forming the navi gable arm of the Tiber (reopened for traffic by Gregory XIII. and again by Paul V.). It was surrounded by extensive ware houses, remains of which may still be seen : the fineness of the brickwork of which they are built is remarkable. The perforated
travertine blocks to which the ships were made fast may still be seen. Farther to the east is a circular building in brick with niches called the temple of Portumnus.
Portus eventually captured the main share of the harbour traffic of Rome, and though the importance of Ostia did not at once decrease we find Portus already an episcopal see in Constan tine's time not very long after Ostia, and the only harbour in the time of the Gothic wars. Its abandonment dates from the partial silting up of the right arm of the Tiber in the middle ages, which restored to Ostia what little traffic was left. To the west of the harbour is the cathedral of S. Rufina (loth century, but mod ernized except for the campanile) and the episcopal palace, forti fied in the middle ages, and containing a number of ancient in scriptions from the site. On the island (Isola Sacra) just opposite is the church of S. Ippolito, built on the site of a Roman building, with a picturesque 13th century campanile; 2 m. to the west is the modern village of Fiumicino at the mouth of the right arm of the Tiber, 21 m. west-south-west by rail from Rome. It is a por tion of the commune of Rome. Three miles to the north is the pumping station by which the lowland (formerly called Stagno di Maccarese, now reclaimed and traversed by many drainage canals) is kept drained (Bonifica di Maccarese).