In 1346 the French focused their effort on the south west and, early in the campaigning season, an army of 15,000–20,000 men marched down the valley of the Garonne.

The garrison, some 900 men, sortied repeatedly to interrupt the French operations, while Lancaster concentrated the main Anglo-Gascon force at La Réole, some 30 miles (48 km) away, as a threat.

Philip VI repeatedly ordered his son, Duke John, to break off the siege and bring his army north.

By August, the French supply system had broken down, there was a dysentery epidemic in their camp, desertion was rife and Philip VI's orders were becoming imperious.

[8] Although Gascony was the cause of the war, Edward was able to spare few resources for it and whenever an English army campaigned on the continent it had operated in northern France.

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.

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.

[14][15] 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.

[18] John, Duke of Normandy, the son and heir apparent of Philip VI, was placed in charge of all French forces in south west France, as he had been the previous autumn.

In spite of borrowing over 330,000 florins (£61,000,000 in 2025 terms[note 3]) from the Pope, Duke John had to issue orders to local officials to: "Amass all of the money you can for the support of our wars.

[19][20] Duke John planned to march on and besiege the large, strongly fortified town of La Réole on the north bank of the Garonne river, only 35 miles (56 km) from Bordeaux, which Lancaster had captured the previous year.

[17][21] Lancaster understood that no French offensive could have a permanent effect so long as Aiguillon, described by the modern historian Kenneth Fowler as "the key to the Gascon plain",[22] was held, so he garrisoned it very strongly: 300 men-at-arms and 600 archers commanded by Stafford.

Duke John employed over 300 carpenters in its construction, escorted by 1,400 crossbowmen and an unknown but significant number of men-at-arms.

[17][24][29] As was normal, within a matter of days the large French army had swept the surrounding area clear of supplies, and so was entirely dependent on the rivers for its logistics.

The Anglo-Gascon army based in La Réole harassed the French foragers, intercepted their supplies and kept them in a constant state of alarm.

[17] The French army began to starve; horses died for lack of fodder; the dysentery epidemic worsened; cases of desertion, increasingly to the English, mounted.

[34] In 1345 Edward III had sent expeditionary forces to Gascony and Brittany and had assembled his main army for action in northern France or Flanders.

[38] To guard against any possibility of an English landing in northern France, Philip VI relied on his powerful navy.

[39] This reliance was misplaced given the naval technology of the time[39][40] and on 12 July an English army of 7,000–10,000 landed near Saint-Vaast-la-Hougue in north west Normandy.

After a furious argument with his advisers, and according to some accounts his father's messenger, Duke John refused to move until his honour was satisfied.

[43] Philip VI sent orders to Duke John insisting that he abandon the siege of Aiguillon and march his army north.

In at least the early stages of their retreat, discipline amongst the French was poor; there are accounts of men being jostled off the bridge over the Garonne and drowned.

[48] After Crécy the French stripped their garrisons in the south west to build-up a new army to face the main English threat in the north east.

Local Gascon forces besieged the few major strongholds in the Bazadais region still held by the French; they were all taken, including the town of Bazas.

[49] Further Gascon forces raided to the east, deep into Quercy, penetrating over 50 miles (80 km); the modern historian Jonathan Sumption describes this as "dislocating the royal administration in central and southern France for three months".

[50] Meanwhile, Lancaster himself took a small force, 1,000 men-at-arms and an unknown number of archers (possibly 1,000), 160 miles (260 km) to the north on a grand chevauchée, a great mounted raid, during which he captured the rich provincial capital of Poitiers, and many towns and castles throughout Saintonge and Aunis.