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A battle in the The Peninsular Campaign.
The siege started on 16 March, with the final assault on 06 April 1812.
Much information on this wiki page and this site.
For a good introduction to the Peninsular Campaign, this site is very good.
See also Duke of Wellington, Napoleon, Frog, French, Sharpe, Talavera, Fuentes Onoro, Salamanca and Yet another occasion when the slovenly Frogs were given a richly deserved slapping