To a large degree military historians live in a fantasy world of "Great Men and Great Armies" doing battle and do books and movies accordingly.
What is often forgotten or ignored is the boring matter of logistics . . . of how those troops were able to get there, of how they were fed and supplied. The fact of the matter is without a strong logistical support system any army would soon be boiling their leather shoes or killing dogs for food.
Strategy and tactics are easy to understand. But the science of equipping and feeding armed forces on campaign is extremely technical, its mysteries understood by only a few initiates. Still more than anything else logistical constraints limit the activities of any army during a war.
For example, in the 19th century the British military had a Land Transportation Corp that at one point had 14,000 men and 28,000 beasts.
The maintenance of Eastern Roman armies and the recruitment and equipping of its military expeditions constituted one of the heaviest burdens on the finances of the Empire. From the 7th to the 12th centuries there is virtually no contemporary evidence of how armies were raised and supplied even though there were numerous campaigns into the Balkans or against the caliphate on the Eastern Front.
The Empire's system of building an extensive and well-maintained road network, as well as its absolute command of the Mediterranean for much of its history allowed the navy to supply troops in widely scattered parts areas and then move men and supplies overland. Forces were routinely supplied via fixed supply chains, and although Roman armies in enemy territory would often supplement or replace this by foraging for food or purchasing food locally.
One historian estimated that a single legion would have required 13.5 tonnes of food per month, and that it would have proved impossible to source this locally.
It is clear from these texts that the basic fiscal mechanisms in the sixth and the ninth centuries were almost identical: the terminology had changed, and the administrative relationships between the different departments responsible for the procedure was slightly different, but in essentials the later system was very obviously derived from the earlier. The process by which the evolution of the later process out of the earlier occurred nicely illustrates the degree of systemic continuity between late Roman and middle Byzantine practices.
Armies were usually accompanied by a supply-train; the late tenth-century treatise on campaign organization stipulates a basic supply of 24 days’ rations of barley for the horses, which according to other sources was similarly to be put aside by the thematic prôtonotarios for collection by the army en route; and historians’ accounts of campaigns frequently mention the baggage-train or the supplies and fodder it carried.
Smaller units clearly foraged for their own fodder and supplies, whether in enemy territory or on Roman soil, which must have caused some hardship to the communities affected; while once on hostile terrain the commander must either have arranged to keep his supply-lines open by detaching small units to hold key passes and roads, or let the army forage for all its requirements once the supplies had run out.
Leo VI advised generals to carry sufficient supplies with the army and to forage on enemy territory rather than prey upon the citizens of the Empire; the need to avoid harming the provincials by permitting the army to forage and extract supplies without proper administrative controls is often repeated.
The average length of a day’s march for infantry or combined forces was probably rarely more than twelve – fourteen miles. The distances at which supply dumps could be established or stops made to feed and water men and animals was also directly related to the distance covered in a day’s march.