Arsĭa, ae, m.,
a small river of Istria , which became the boundary between Italy and Illyricum under Augustus; the present Arsa , Plin. 3, 26, 29, § 150; Flor. 2, 5; cf. Mann. Thrace, p. 325.
A´RSIA a small river of Istria, still called Arsa, which became the boundary between Italy and Illyr...
Dictionary of Greek and Roman Geography