The epistolary heritage of Synesius of Cyrene, bishop of Ptolemais and the most distinguished representative of the so-called «Hellenic Christianity», may be considered as the main source on the military history of Late Roman Cyrenaica in the first third of the 5th c. AD. But the problem of these data consists in narrow chronological limits of Synesius’ correspondence and inaccuracies of his military terminology. The author of the present paper used the evidence of inscriptions and papyri to trace the history of the military units mentioned in Synesius’ letters. The comparative analysis led the author to the conclusion that up to 394 AD Cyrenaica had no regional (local) army of its own, and all military campaigns against the local nomadic tribes were carried out by the troops moved to Pentapolis only temporarily. It was not until 394 AD that a new military corps was set in Libya in the frameworks of preparing a probable campaign in North Africa, and this corps was composed from various cavalry and infantry detachments. These units had the status of frontier garrisons (limitanei) and had been dislocated in Egypt or Near Eastern provinces. The author maintains that even after this transfer to Cyrenaica they did not change their status and continued to be limitanei.