Legio III Isaura was a pseudocomitatensis Roman legion

Roman legion

A Roman legion normally indicates the basic ancient Roman army unit recruited specifically from Roman citizens. The organization of legions varied greatly over time but they were typically composed of perhaps 5,000 soldiers, divided into maniples and later into "cohorts"...

, levied no later than under Diocletian

Diocletian

Diocletian |latinized]] upon his accession to Diocletian . c. 22 December 244  – 3 December 311), was a Roman Emperor from 284 to 305....

, and possibly already present under Probus. As their name suggests, III Isaura and its twin legion II Isaura

Legio II Isaura

Legio II Isaura was a pseudocomitatensis Roman legion, levied no later than under Diocletian, and possibly already present under Probus. As their name suggests, II Isaura and its twin legion III Isaura were guarding the Isauria territory at the time of the Notitia Dignitatum, to defend it from the...

 were guarding the Isauria

Isauria

Isauria , in ancient geography, is a rugged isolated district in the interior of South Asia Minor, of very different extent at different periods, but generally covering what is now the district of Bozkır and its surroundings in the Konya province of Turkey, or the core of the Taurus Mountains. In...

 territory at the time of the Notitia Dignitatum

Notitia Dignitatum

The Notitia Dignitatum is a unique document of the Roman imperial chanceries. One of the very few surviving documents of Roman government, it details the administrative organisation of the eastern and western empires, listing several thousand offices from the imperial court down to the provincial...

, to defend it from the incursions of the mountain peoples. It is possible that in the beginning they were supported by I Isaura Sagittaria.