Unlike other historical eras, logistics in the Middle Ages has not been intensively studied, though increasingly scholars have begun paying more attention to it. The purpose of military logistics in the medieval world was to ensure an army’s survival, but not its comfort. In static warfare over fortifications, defending forces could, with ample warning of an enemy’s approach, gather foodstuffs which would allow them to hold out for months. By gathering up resources garrisons denied them to approaching field armies. Unless a shortage of water occurred, or the food supply failed or was spoiled or destroyed, or the fortification fell by direct assault, the defenders had an excellent chance of waiting out any army trying to besiege them. Field armies, on the other hand, had to trace back through rivers and roads a line of supply that could only be as long as the chain of fortifications they controlled along those routes. As was often the case, not being able to trace a line of supply meant that a field army’s days were numbered in any given campaign season, and the army would melt away as it quickly consumed its own supplies.
In terms of the logistical difficulties of both sides in the Occitan War, the forces of the crusade had a much greater challenge. The southern side possessed interior lines, access to and knowledge of the countryside, and inhabitants who usually supported resistance to the crusade. Besieging armies from the north had to maintain their supplies without these advantages. Travel along the roads was dangerous and crusader supply trains required heavy escorts which very often drained the army of its most mobile soldiers. For example, the battle of Saint Martin-la-Lande in 1211 occurred when Simon of Montfort had to rescue a supply train which had been trapped by a southern army. Unless the season was right and food and fodder could be procured along the line of march, a supply train of pack or draft animals had to carry its own feed to the detriment of human foodstuffs, and this made supply difficult in regions with a weak agricultural base such as Termes or Cabaret high in the Black Mountains. If pack animals are dependent solely on what they carry on their backs they will consume it within ten days. A pack train whose animals graze for fodder but transport their own grain will eat up everything they carry within twenty-five days assuming they carry nothing else. A pack train carrying human food, grain, fodder, and non-comestibles therefore had to reach its objective in far less time in order to be effective.
Even though Occitania had abundant navigable rivers, overall control along their length fell to communities often sympathetic to the southern cause. The crusade could not control every town, and therefore its supply line along a river was always vulnerable. The geographical location of rivers in the region did not always make supply convenient for an army marching away from a river. Control of a river could prove vital to victory or defeat, as Simon of Montfort found out at the siege of Beaucaire in 1216 and the second siege of Toulouse in 1217–18, where the crusade could neither check enemy boat traffic nor supply itself because it did not command the entire length of the river. Distance from navigable rivers meant that places like Termes or Cabaret were absolute nightmares when keeping a besieging army supplied. The only way up to fortifications such as these was so steep that resupply was restricted to single-file pack animals and human porters. With few exceptions, the crusaders during the Occitan War were as miserable and ill-fed if not more so than the people they inflicted war upon.