OSTIA, an ancient town and harbour of Latium, Italy, at the mouth of the river Tiber on its left bank. It lies 14 m. S.W. from Rome by the Via Ostiensis, a road of very ancient origin still followed by a modem road which preserves some traces of the old pavement and remains of several ancient bridges. It was the first colony ever founded by Rome - according to the Romans themselves, by Ancus Martius - and took its name from its position at the mouth (ostium) of the river. Its origin is connected with the establishment of the salt-marshes (salinae - see Salaria, Via) which only ceased to exist in 1875, though it acquired importance as a harbour in very early times. When it began to have magistrates of its own is not known: nor indeed have we any inscriptions from Ostia that can be certainly attributed to the Republican period. Under the empire, on the other hand, it had the ordinary magistrates of a colony, the chief being diwviri, charged with the administration of justice, whose place was taken every fifth year by duoviri censoria potestate quinqiiennales, then quaestores (or financial officials) and then acdilcs (building officials). There were also the usual decuriones (town councillors) and Augustales. We learn much as to these magistrates from the large number of inscriptions that have been found (over 2000 in Ostia and Portus taken together) and also as to the cults. Vulcan was the most important - perhaps in early times the only - deity worshipped at Ostia, and the priesthood of Vulcan was held sometimes by Roman senators. The Dioscuri too, as patrons of mariners, were held in honour. Later we find the worship of Isis and of Cybele,the latter being especially flourishing, with large corporations of dendrophori (priests who carried branches of trees in procession) and cannofori ( basketcarriers); the worship of Mithras, too, had a large number of followers. There was a temple of Serapis at Portus. No traces of Jewish worship have been found at Ostia, but at Portus a considerable number of Jewish inscriptions in Greek have come to light.
Of the church in Ostia there is no authentic record before the 4th century A.D., though there are several Christian inscriptions of an earlier date; but the first bishop of Ostia of whom we have any certain knowledge dates from a.d. 313. The see still continues, and is indeed held by the dean of the sacred college of cardinals. A large number of the inscriptions are also connected with the various guDds - firemen (cenlonarii), carpenters and metal workers (fabri), boatmen, lightermen and others (see J. P. Waltzing, Les Corporations projessionelles, Brussels and Liege) .
Until Trajan formed the port of Centumcellae (Civitavecchia) Ostia was the best harbour along the low sandy coast of central Italy between Monte Argentario and Monte Circeo. It is mentioned in 354 B.C. as a trading port, and became important as a naval harbour during the Punic Wars. Its commerce increased with the growth of Rome, and this, and the decay of agriculture in Italy, which obliged the capital to rely almost entirely on imported corn (the importation of which was, from 267 B.C. onwards, under the charge of a special quaestor stationed at Ostia), rendered the possession of Ostia the key to the situation on more than one occasion (87 B.C., a.d. 409 and 537). The inhabitants of the colony were thus regarded as a permanent garrison, and at first freed from the obligations of ordinary military service, until they were later on obliged to serve in the fleet. Ostia, however, was by no means an ideal harbour; the mouth of the Tiber is exposed to the south-west wind, which often did damage in the harbour itself; in a.d. 62 no less than 200 ships with their cargoes were sunk, and there was an important guild of divers (uritiatorcs) at Ostia. The difficulties of the harbour were increased by the continued silting up, produced by the enormous amount of solid material brought down by the river. Even in Strabo's time (v. 3. 5, p. 231) the harbour of Ostia had become dangerous: he speaks of it as a " city without a harbour owing to the silting up brought about by the Tiber . . . : the ships anchor at considerable risk in the roads, but the love of gain prevails: for the large number of lighters which receive the cargoes and reload them renders the time short before they can enter the river, and having lightened a part of their cargoes they sail in and ascend to Rome."
Caesar had projected remedial measures, but (as in so many cases) had never been able to carry them out, and it was not until the time of Claudius that the problem was approached. That emperor constructed a large new harbour on the right bank, 25 m. N. of Ostia, with an area of 170 acres enclosed by two curving moles, with an artiflcial island, supporting a lofty lighthouse, in the centre of the space between them. This was connected with the Tiber by an artiflcial channel, and by this work Claudius, according to the inscriptions which he erected in a.d. 46, freed the city of Rome from the danger of inundation. The harbour was named by Nero, Portus Augusti.
Trajan found himself obliged in a.d. 103, owing to the silting up of the Claudian harbour, and the increase of trade, to construct another port further inland - a hexagonal basin enclosing an area of 97 acres with enormous warehouses - communicating with the harbour of Claudius and with the Tiber by means of the channel already constructed by Claudius, this channel being prolonged so as to give also direct access to the sea. This became blocked in the middle ages, but was reopened by Paul V. in 1612, and is stiU in use. Indeed it forms the right arm of the Tiber, by which navigation is carried on at the present day, and is known as the P'ossa Trajana. The island between the two arms acquired the name of Insula Sacra (still called Isola Sacra) by which Procopius mentions it.
Ostia thus lost a considerable amount of its trade, but its importance still continued to be great. The 2nd and 3rd centuries, indeed, are the high-water mark of its prosperity: and it still possessed a mint in the 4th century a.d. During the Gothic wars, however, trade was confined to Portus, and the ravages of pirates led to its gradual abandonment. Gregory IV. constructed in 830 a fortified enceinte, called Gregoriopohs, in the eastern portion of the ancient city, and the Saracens were signally defeated here under Leo IV. (847-856). The battle is represented in Giulio Romano's fresco from Raphael's design in the Stanza deU' Incendio in the Vatican.
In the middle ages Ostia regained something of its importance, owing to the silting up of the right arm of the Tiber. In i4iS3- 1486 Giuliano della Rovere (nephew of Pope Sixtus IV., and afterwards himself Pope Julius II.) caused the castle to be erected by Baccio Pontelli, a little to the east of the ancient city. It is built of brick and is one of the finest specimens of Renaissance fortification, and exemplifies especially the transition from the old girdle walls to the system of bastions; it still has round corner towers, not polygonal bastions (Burckhardt). Under the shelter of the castle lies the modern village. The small cathedral of St Aurea, also an early Renaissance structure, with Gothic windows, is by some ascribed to Meo del Caprina (1430-1501). Hitherto Ostia does not seem to have been very unhealthy. In 1557, however, a great flood caused the Tiber to change its course, so that it no longer flowed under the wails of the castle, but some half a mile farther west; and its old bed (Fiume Morto) has ever since then served as a breeding ground for the malarial mosquito (Anopheles claviger). An agricultural colony, founded at Ostia after 1875, and consisting mainly of cultivators from the neighbourhood of Ravenna, has produced a great change for the better in the condition of the place. The modern village is a part of the commune of Rome. The marshes have been drained, and a pumping station erected near Castel Fusano. An electric tramway has been constructed from Rome to Ostia and theijce to the seashore, now some 2 m, distant, where sea-bathing is carried on.
Excavations on the site of Ostia were only begun towards the close of the 18th century, and no systematic work was done until 1854, when under Pius IX. a considerable amount was done (the objects are now in the Lateran museum). The Italian government, to whom the greater part of it now belongs, laid bare many of the more important buildings in 1880-1889; but much was left undone. Owing to the fact that the site is largely covered with sand and to the absence of any later alterations, the preservation of the buildings excavated is very good, and Ostia is, with the exception of Pompeii, the best example in Italy of a town of the Roman period. On the east the site is approached by an ancient road, flanked by tombs. On the right (N.) are some small well-preserved thermae, and the barracks of the firemen (vigiles),a. special cohort of whom was stationed here. On one side of the central courtyard of the latter building is a chapel with inscribed pedestals for imperial statues (2nd and 3rd century a.d.) and a well-preserved black and white mosaic representing a sacrifice (see J. Carcopino in Melanges de V Ecole FranQaise, 1907).
To the south-west is the Forum, an area 265 ft. square surrounded by colonnades, in which were placed the offices of the various collegia or guilds of boatmen, raftmcn and others, which had a special importance at Ostia; the names of the guilds may still be read in inscriptions in the mosaic pavements of the chambers. In the centre of the area are the substructions of a temple, and on the south-east side are the remains of the theatre, built in the early imperial period, restored by Septimius Severus in 196-197 and again in the 4th or 5th century. To the south-west of the Forum are the remains of three small temples, one dedicated to Venus, and a well-preserved Mithraeum, with mosaics representing the seven planets, etc. To the south-west again is the conspicuous brick cella of a lofty temple, on arched substructures, generally supposed to be that of Vulcan, with a threshold block of africano (Euboean) marble over 15 ft. long: from it a street over 20 ft. wide leads northwest to the river. It is flanked on each side by weU-preserved warehouses, another group of which, surrounding a large court, lies to the south-west. The brick and opus retiadalum facing of the walls is especially fine. Hence an ancient road, leading between warehouses (into which the Tiber is encroaching), in one room of which a number of weU-preserved large jars may be seen embedded in the floor, runs close to the river to a large private house with thermae, in which five mosaics were found: it (groundlessly) bears the name of " imperial palace." Farther to the south-west are remains of other warehouses, and (possibly) of the docks - long narrow chambers, which may have served to containships. Hereare remainsof (earlier) structures in opiis qiiadralum whereas the great bulk of the ruins are in brickwork and belong to the imperial period. The medieval Torre Boacciana marks approximately the mouth of the river in Roman times.
The south-eastern portion of the city has been excavated only very partially. To the south-west of the conspicuous temple alluded to are the remains of a temple of Cybele, with a portico. This lay close to the commencement of the Via Severiana (sec Sevekiana, Via), and the line of tombs which flanked it soon begins. Farther south-east, a line of sand dunes, covering the ruins of ancient villas, marks the coastline of the Roman period. .Some 2 m. to the south-east is the pine forest of Castel Fusano, taking its name from a castle erected by the marchese Sacchetli in the 16th century. It is now the property of the Chigi and is leased to the king (see Laurentina, Via). Here Drs Lowe and Sambon made the decisive experiments which proved that the propagation of malaria was due to the mosquito .lMo/)/if/Mc/(;:'/^fr.
See Notizie dcgli scavi, passim: H. Dessau in Corp. inscript. Latin, xiv. (Berlin, 1887), pp. i sqq., and the works of M. Jerome Carcopino. (T. As.)
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)