89. 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.