The territory of the Osismii was located at the extremity of the
Brittany Peninsula, west of the
Veneti and
Coriosolites. According to the consensus view summarised by Patrick Galliou, following Pierre Merlat and François Merlet, the territory of the Osismii extended across most of modern
Finistère, parts of the
Côtes-d'Armor (with
Trégor and Goëlo regions), and slightly into
Morbihan. It was bounded roughly from the
Gouët estuary at
Saint-Brieuc in the north to the
Ellé at
Quimperlé in the south, a distribution corroborated by the spread of their pre-Roman coinage. Their chief town was Vorgium (present-day
Carhaix), which the
Tabula Peutingeriana places at the tip of the Armorican peninsula. Ptolemy names
Vorganium as the chief town of the Osismii. However, a milestone from northern Finistère suggests that
Vorganium more likely refers instead to Kérilien (in
Plounéventer), which was a different settlement in Gallo-Roman times and makes Ptolemy's identification probably incorrect. Scholars often attribute the decline of Vorgium to a transfer of capital status. The creation of the
Tractus Armoricanus prompted the construction of coastal fortifications against Saxon piracy, shifting strategic priorities toward the coast and leading to the erection of a major
castellum at Brest. In the early Middle Ages, Brest appears under the names
Civitas Osismorum and
Urbs Osismi, probably derived from a 4th-century
Osismis mentioned in the
Notitia Dignitatum. == History ==