In the second volume of his History of the Art of War, Hans Delbrück devotes a chapter in book three to the military organization of the early Byzantine/late Roman Empire under the emperor Justinian. He examines the dissolution of discipline within the ranks, as well as the transition to a generally cavalry centered army. This more mobile force than the famous legions of previous epochs – particularly the republican one – was the culmination of centuries of evolution within the Roman army that had commenced under the emperor Gallienus. The resultant innovations from this transformation would give Justinian the edge in escalation dominance over the barbarian kingdoms in the West, and would open-the-door to a Roman re-conquest of North Africa, Sicily, and the Italian peninsula – all within the span of forty years.
“The active armies were quite small. Belisarius had 25,000 men when he won his victory over the Persians at Daras in 530. He landed in Africa with no more than 15,000 men, and of these 15,000, the 5,000 cavalry included in that total were sufficient to defeat the Vandals in the open field. Even smaller was the army with which Belisarius moved to Italy in order to destroy the East Gothic Kingdom eleven years after Theodoric’s death: there were no more than 10,000 to 11,000 men.
“A contemporary author, Agathias (5. 13), estimated that the total Roman army must have been 645,000 men strong but that only 150,000 men were actually available under Justinian.
“A very large number of the soldiers with whom Belisarius had conquered Italy deserted to the Goths when, after he was relieved, the Roman domination again collapsed and Totila established the Gothic kingdom.
“After the fourth century A.D., and after the disappearance of the legions, everything changed. The barbarian mercenaries now felt that they were the masters. Woe to the prince or the general who might have dared to incur their displeasure by his strictness!
“Procopius considers it a half-miracle and an extraordinary accomplishment of Belisarius that the Romans marched into Carthage in good order, ‘whereas otherwise the Roman troops never march into their own cities without disorder, even if there are only 500 of them.
*All excerpts have been taken from History of the Art of War, Volume II: The Barbarian Invasions, Hans Delbrück, University of Nebraska Press.