The capital of the Segusini was Segusio (modern Susa, in Piedmont), which voluntarily became part of the Roman Empire in the late 1st century BC. Segusio was also the capital of the province Alpes Cottiae. According to the medieval historian Rodulfus Glaber, Segusio was "the oldest of Alpine towns".
On the French side of Alpis Cottia (Mont Genèvre), Brigantium (modern Briançon) was, according to Ptolemy, within the limits of the Segusini. Brigantium had also formed part of the kingdom of King Cottius and was also in the ancient Roman province of Alpes Cottiae. The Tabula Peutingeriana places Brigantium 6 MP (Roman miles) from Alpis Cottia. The Jerusalem Itinerary makes the Alpes Cottiae commence at Rama between Ebrodunum (modern Embrun) and Brigantium.