The many sieges of the Napoleonic Wars remain a relatively neglected area of historical study, especially in the context of the history of customary laws of war, where sieges played a central role. This article explores an important but largely forgotten episode in the infamous British storm and sack of the French-held Spanish towns of Ciudad Rodrigo, Badajoz and San Sebastián during the Peninsular War: mercy to the French garrisons, who, in obstinately defending against storming parties, had forfeited their protective rights under prevailing laws of war. Combining military, legal and cultural history, and drawing upon British soldiers’ letters, diaries and memoirs, the article focuses on three interrelated issues: siege capitulation and su...