Since the Norman Conquest of 1066, English monarchs had held titles and lands within France, the possession of which made them vassals of the kings of France. By 1337 only Gascony in southwestern France and Ponthieu in northern France were left. The independent-minded Gascons preferred their relationship with a distant English king who left them alone to one with a French king who would interfere in their affairs. Following a series of disagreements between Philip VI of France (r. 1328–1350) and Edward III of England (r. 1327–1377), on 24 May 1337 Philip's Great Council agreed Gascony should be taken back into Philip's hands, on the grounds that Edward was in breach of his obligations as a vassal. This marked the start of the Hundred Years' War, which was to last 116 years.
France in 1330
Under French royal control in 1214
Gained from English control by 1330
England and English-controlled Gascony in 1330
Before the war commenced, well over 1000 ships a year departed from Gascony. Among their cargoes were over 200,000,000 imperial pints (1,100,000 hectolitres; 240,000,000 US pints) of locally produced wine. The duty levied by the English Crown on wine from Bordeaux was more than all other customs duties combined and by far the largest source of state income. Bordeaux, the capital of Gascony, had a population of over 50,000, greater than London's, and was possibly richer. However, by this time English Gascony had become so truncated by French encroachments that it relied on imports of food, largely from England. Any interruptions to regular shipping were liable to starve Gascony and financially cripple England; the French were well aware of this.
The border between English and French territory in Gascony was extremely unclear. 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 fortified tower or keep, with larger estates having 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 frequently. 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.
Although Gascony was the cause of the war, in most campaigning seasons the Gascons had had to rely on their own resources and had been hard pressed by the French. In 1339 the French besieged Bordeaux, the capital of Gascony, 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 infantry, although up to two-thirds of them would be tied down in garrisons. Warfare was usually a struggle for possession of castles and other fortified points, and for the mutable loyalty of the local nobility.
A medieval town under assault (15th-century miniature)
By 1345, after eight years of war, English-controlled territory mostly consisted of a coastal strip from Bordeaux to Bayonne, with isolated strongholds further inland. In 1345 Edward III had sent Henry, Earl of Lancaster to Gascony, and had assembled his main army for action in northern France or Flanders. It had sailed but never landed, after the fleet was scattered in a storm. Knowledge of Edward III's intent had kept French focus on the north until late in the campaigning season. Meanwhile, Lancaster[note 1] had led a whirlwind campaign at the head of an Anglo-Gascon army. He had smashed two large French armies at the battles of Bergerac and Auberoche, captured French towns and fortifications in much of Périgord and most of Agenais and given the English possessions in Gascony strategic depth. During the winter following this successful campaign, Lancaster's second in command, Ralph, Earl of Stafford, had marched on the vitally important town of Aiguillon, which commanded the junction of the Rivers Garonne and Lot, making it important both for trade and for military communications. The inhabitants had attacked the garrison and opened the gates to the English.