Conceived by Thomas Burberry for the English officers in the First World War, the trench coat, as waterproof as it is elegant, came with the soldiers into town when the war was over, and ended up seducing civilians. Immortalised by Humphrey Bogart in Casablanca in 1942, it became - with its under collar flap, where once before the butt of a rifle rested, its ten double breasted buttons, its belt and epaulettes - the uniform of detectives and an eternal ally of elegant men.