Murray organized his army into one Spanish and two British infantry divisions, some cavalry, 2 British and 1 Portuguese field artillery batteries, plus some unassigned units. General William Clinton's 1st Division was made up of the 1/58th Regiment of Foot and 2/67th Regiment of Foot, the 4th King's German Legion and 2 battalions of the Sicilian "Estero" Regiment. General John Mackenzie's 2nd Division was made up of the 1/10th Regiment of Foot, 1/27th Regiment of Foot and 1/81st Regiment of Foot, De Roll's Swiss and the 2nd Italian Regiment. The cavalry force included two squadrons each of the 20th Light Dragoons and the Brunswick Hussars. The Calabrian Free Corps and the 1st Italian Regiment were unbrigaded. Murray's 18 heavy siege guns were the same ones that Wellington used to breach the walls during the siege of Ciudad Rodrigo and at the Battle of Badajoz in 1812. Rufane Shaw Donkin served as Murray's chief-of-staff.