The Castillonais or Cheval Ariègeois de Castillon , also formerly called Cheval du Biros or Saint-Gironnais, is an ancient breed of small rustic saddle-horse from the Ariège département of south-western France. It may be dark bay or seal brown. It stands 135–155 centimetres at the withers, with an average height of about 145 cm. It is used principally for trekking and for driving.