Ney's VI Corps made up part of a 65,000-strong army commanded by André Masséna, who was bent on a third French invasion of Portugal.

[2] Viscount Wellington was not however prepared to meet the French in open battle, as he was greatly outnumbered, resting on the Portuguese frontier to await the outcome of the siege.

Herrasti's 5,500-man Spanish garrison put up a gallant and sustained defence,[2] for over ten weeks, surrendering only after the counterscarp had been blown in, Ney's artillery opened practical breaches in the walls and the French infantry were poised for an assault.

The lines were designed to enable a successful defence of Lisbon and avoid a British evacuation of the peninsular, as had happened after the Battle of Corunna in January 1809.

The delay in capturing Ciudad Rodrigo gave many precious weeks of time to enable the Lines of Torres Vedras to be completed and therefore contributed greatly to the Allied victory of the Peninsular War.