The Ostia Tiberina (see Cluver. Italia Antiq. 1. iii. p. 870-879), in the plural number, the two mouths of the Tiber, were separated by the Holy Island, an equilateral triangle, whose sides were each of them computed at about two miles. The colony of Ostia was founded immediately beyond the left, or southern, and the Port immediately beyond the right, or northern, branch of the river; and the distance between their remains measures something more than two miles on Cingolani's map. In the time of Strabo the sand and mud deposited by the Tiber had choked the harbour of Ostia; the progress of the same cause has added much to the size of the Holy Island, and gradually left both Ostia and the Port at a considerable distance from the shore. The dry channels (fiumi morti) and the large estuaries (stagno di Ponente, di Levante) mark the changes of the river and the efforts of the sea. Consult, for the present state of this dreary and desolate tract, the excellent map of the ecclesiastical state by the mathematicians of Benedict XIV.; an actual survey of the Agro Romano, in six sheets, by Cingolani, which contains 113,819 rubbia (about 570,000 acres); and the large topographical map of Ameti, in eight sheets.