The fortress was garrisoned by 1,400 French troops under General Brennier. The investing force varied but was in the region of 13,000 men. Massena's attempt to lift the siege resulted in his defeat at the battle of Fuentes de Oñoro. The British did not take the fortress because the French garrison threaded its way through the British lines on the night of the 10/11 May leaving fuses burning so that the fortress was blown up.
Wellington was extremely angry at the stupidity of the investing forces.

The fortress of Almeida about 10 miles from the Spanish border inside Portugal a little north of the latitude of Madrid. (Portugal)