[6] It saw a Franco-Spanish garrison in the fortified town of Mons, then in the Spanish Netherlands, besieged by a force of the Duke of Marlborough's Grand Alliance army under the command of the Prince of Orange.

Villars had expected the Allies to move north-west against Ypres and hastily re-evaluated his plan, seeking permission from Louis XIV for offensive action.

[10][1] The garrison was made up of mainly Spanish troops, with smaller numbers of Bavarians and French who Villars had ordered to join the defenders when Tournai fell.

[15] Following the neutralisation of the French threat, Marlborough and Eugene directed a force under the Prince of Orange to surround the city of Mons, which was done on 19 and 20 September.

[12] Boufflers received orders from Louis to not risk another battle, and therefore no attempt was made by the French to relieve Mons once the siege was underway.

On 10 October, Marlborough wrote to the Earl of Sunderland from his camp at Havré to express his frustration at the weather's impact on the siege's progress.

[19] At noon on 20 October, observing the Allied preparations for an assault supported by artillery, Grimaldi sounded the chamade and signalled his intention to surrender.

[7] On 23 October, the Franco-Spanish accepted the Allied terms of capitulation and the garrison's remaining 1,500 men left Mons with the honours of war but without their cannon or mortars.

Owing to heavy French and Allied loses at Malplaquet, the capture of Mons marked the final engagement of the 1709 campaign season in the war.