The Raša rises in springs near Pićan and flows south through a steep-sided valley before opening into the head of the Adriatic Sea.

[3] By Roman times, the Arsia, as it was called in Latin, constituted the border between the Histri, who lived west of its banks, and the Liburni on the coast to the east,[4] with the Iapydes in the upcountry valley behind them.

In the early 10th century Tomislav of Croatia ruled a state that ran from the Adriatic to the Drava, and from the Raša, as it was now being called, to the Drina.

[4][9] In the 13th century, the territory on the east bank was administered by the counts of Gorizia, while that on the west was ruled by the patriarchs of Aquileia.

The planned city of Raša (Italian: Arsia), on the tributary Krapanski Potok of the river in the inner part of the Raška Inlet, was constructed in 1936–1937 as Arsia on drained wetlands to gain arable land for farming and to serve expanding coal mining operations, as part of Mussolini's urban colonization and Italianization of Istria.