The present paper deals with three important points of the organizational structure of the Byzantine army under the reign of Heraclius during his military campaigns against the Persians: 1) the revolt of general Comentiolus against Heraclius and the impact of this event on the development of the Eastern Byzantine army; 2) the original composition of the army of Opsikion, which garrisoned in Constantinople and 3) the rank and legal status of military units, which defended the imperial Near East frontier against the Persian invasions in 610-614 A.D. The author analyzed narrative sources (“The Life of Theodore of Sykeon”, “The Capture of Jerusalem”, “The Miracles of Saint Anastasius” and other) and epigraphic data (epitaphs from Constantinople published in 1995). On the basis of their information, the author came to the conclusion that the revolt of Comentiolus influenced negatively the further development of the Eastern Byzantine army: many of its units moved to Asia Minor after 610 as a result of this revolt, correspondingly, the strength of this army diminished considerably. After 610 the Near East was defended only by a number small garrisons, each one consisting of about 500 men. In spite of this fact, since about 610 the gradual rising of the army of Opsikion began. The author demonstrates that its original composition included the guard palace regiments, which were located in the Byzantine capital: the palace scholae , the body of excubitores , the detachments of so-called bucellarii , groups of foederati and units of the former central field-armies ( praesentales ), which had served in Constantinople at an earlier period.