Siege of Almeida ( 1810 ) In the Siege of Almeida , the French corps of Marshal Michel Ney captured the border fortress from Brigadier General William Cox ' s Portuguese garrison . This action was fought in the summer of 1810 during the Peninsular War portion of the Napoleonic Wars . Almeida is located in eastern Portugal , near the border with Spain . Background . Lying on a main invasion route from Ciudad Rodrigo to Lisbon , the small fortress was invested by a 65 , 000 - man army under Marshal André Masséna in the third French invasion of Portugal . The previous day the French forces had pushed back the British Portuguese army at the Battle of the Côa . The 50 , 000 - man British - Portuguese army of General Arthur Wellesley , 1st Duke of Wellington now held the far bank of the Coa . However , the rivers banks were steep , with only two bridges , and the French 6th Corps guarded the crossings , so the British were unable to retake the crossings to relieve Almeida . Siege . Fresh from the successful siege of Ciudad Rodrigo , the French army laid siege to Almeida on July 25 , 1810 . Brigadier - General William Cox commanded a 4 , 000 - man Portuguese garrison of three battalions of militia , from Arganil , Trancoso and Vizeu . Some regular British forces were also present , including 1 , 200 men of the 24th Line Regiment , a squadron of the 11th Cavalry Regiment and over 400 gunners . The defences of Almeida were in better repair and stronger than Siege of Ciudad Rodrigo ( 1810 ) which the French had recently taken . In particular , there were over 100 artillery pieces , of which 40 were 18 - pounders or heavier , and most were in protected casemates . The siege was conducted by the 14 , 000 infantry , 1 , 000 cavalry , 1 , 000 artillerists and 100 cannon of the VI Corps under the command of Marshal Michel Ney . In addition , Marshal Jean - Andoche Junot lay in reserve nearby with his VIII Corps . The French received siege supplies from Ciudad Rodrigo on August 15 , and started to dig trench lines to the south - east of the town , facing the San Pedro bastion . The siege train was well supplied with guns ; as well as the existing French ones , it also included captured Spanish guns from Ciudad Rodrigo . By August 24 , the French lines had eleven batteries in place , with over 50 guns . Throughout , the Portuguese defenders had fired upon the French , with little effect . When the French bombardment opened on August 26 at 6am , several quarters of the town were quickly set on fire , and the defending guns of the nearest three batteries overwhelmed . However , the defences held . The governor was confident in withstanding the assault , until a shell made a freak hit . The great magazine in the castle had been used through the day to supply the defenders , and at some point a leaky powder keg had left a trail of powder leading up to the courtyard . At around 7pm , one French shell landed in the courtyard , igniting a gunpowder trail that led through the still open door , and set off a chain reaction into the magazine . The ensuing explosion killed 600 defenders and wounded 300 more . The castle that housed the gunpowder was razed and sections of the defenses were damaged , leaving a crater still visible today . Unable to reply to the French cannonade without gunpowder , Cox was forced to capitulate the following day with the survivors of the blast and 100 cannon . The French lost 58 killed and 320 wounded during the operation . The next action was the Battle of Bussaco . Cultural reference . The siege forms the climax of Bernard Cornwell ' s " Sharpe ' s Gold " , in which Richard Sharpe is credited with the destruction of the ammunition magazine , an act intended to deliberately cut short the siege so that he could leave the city and bring Lord Wellington the finances needed to complete the Lines of Torres Vedras .