Military forces could support themselves by foraging so long as they moved on at frequent intervals. If they wished to remain in one place for any length of time, as was necessary to besiege a castle, then access to water transport was essential for supplies of food and fodder, and desirable for such items as siege equipment. Warfare was usually a struggle for possession of castles and other fortified points, and for the mutable loyalty of the local nobility; the region had been in a state of flux for centuries and many local lords served whichever monarch was considered the stronger, regardless of national ties.