In 1339 the French besieged Bordeaux, even breaking into the city with a large force before they were repulsed. Typically the Gascons could field 3,000–6,000 men, the large majority of whom were infantry, although up to two-thirds of them would be tied down in garrisons. There was no formal border between English and French territory. Many landholders owned a patchwork of widely separated estates, perhaps owing fealty to a different overlord for each. Each small estate was likely to have a tower house, larger estates had castles. Fortifications were also constructed at transport choke points, to collect tolls and to restrict military passage; fortified towns grew up alongside all bridges and most fords over the many rivers in the region. 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 country was stronger, regardless of national ties. By 1345, after eight years of war, English-controlled territory mostly consisted of a coastal strip from Bordeaux to Bayonne, and isolated strongholds further inland. The French had strong fortifications throughout what had once been English-controlled Gascony. Several directly threatened Bordeaux: Libourne, to the east allowed French armies to assemble a day's march from Bordeaux; the strongly fortified town of Blaye was situated on the north bank of the Gironde downstream of Bordeaux and in a position to interdict its vital seaborne communications; the fortress of Langon, south of Bordeaux, blocked upstream communication along the Garonne, and facilitated the supply of any French force advancing on Bordeaux. Edward determined early in 1345 to attack France on three fronts. The Earl of Northampton would lead a small force to Brittany, a slightly larger force would proceed to Gascony under the command of Henry, Earl of Derby and the main force would accompany Edward to either northern France or Flanders. The previous Seneschal of Gascony, Nicholas de la Beche, was replaced by the more senior Ralph, Earl of Stafford, who sailed for Gascony in February with an advance force.