The garrison however, under the Marquis de Surville, held out for considerably longer than had been expected and the siege consumed much of the fighting season.

[4] At the beginning of the 1709 campaign, the Allies were eager to maintain the pressure on Louis XIV by breaking through the line of border fortresses, known as the "Pré carré", and advancing into northern France.

However, the Allied commander, Marlborough, considered the positions held by the French Duke of Villars too strong for a frontal assault.

The garrison consisted of 13½ battalions (9 of them regular line infantry), 5 free corps, 2 artillery companies and 2 Irish brigades, for a total of approximately 7,700 men.

[4] As Marlborough and Eugène's forces marched on Tournai the Prince of Orange was tasked with capturing Mortange and Saint-Amand, to safeguard the siege operations against French attacks from the side of Valenciennes.

[11] On the night of 28 to 29 June, Prince Eugène ordered the construction of bridges over the swampy ground surrounding the Tournai to enable communication between Allied positions on both banks of the Scheldt river.

[3][13] The Allied force was mainly made up of British, Austrian, Prussian and Dutch soldiers, with smaller numbers of Danish, Hessian and Hanoverian troops.

In response to the Allied arrival outside the city, Surville had all of the water locks blocked, causing the river to accumulate in such a way that made getting between the two banks of the Scheldt nearly impossible.

[16] The shelling of Tournai finally began on 13 July and within a week the besiegers managed to drive the French out of their entrenchments in front of the citadel.

Surville held a council of war where it was decided to surrender the city and to retreat to the citadel with what was left of the garrison (approximately 4–5,000 out of 7,700 French soldiers).

In the meantime a temporary armistice was agreed between the parties, while Surville sent the Marquis de Ravignan to Versailles to obtain orders from Louis XIV.

Shortly after the surrender of the city, Marlborough relocated his camp to Orchies, 19km south-west of Tournai, so that he could better monitor the movements of Villars' army.

[9][page needed] With food supplies running low, on 31 August, Surville offered to surrender to Marlborough, but the Allied commanders rejected his proposals.

The French garrison, now numbering no more than 2,400 men, left the citadel with the honours of war and returned to France as part of a prisoner exchange.

[24] Villars was furious at the loss of Tournai and it ended his hopes that the siege would keep Marlborough occupied for the rest of the campaign season.

Despite the vigorous French defence resulting in over 5,000 Allied casualties, Surville quickly lost Louis XIV's confidence and he was dismissed from service.

[23] Having assumed Tournai would hold out until at least October and thus consume the entire 1709 campaign season, Louis now ordered Villars to prevent the loss of Mons "at all costs... the salvation of France is at stake".

Churchill wrote that "the fall of Tournai was followed by an explosion of war-fury strangely out of keeping with the policy and temper in which the campaign had hitherto been conducted".