This building was constructed in the 18C following the plans of William Kent, with two wings enclosing a square where the Changing of the Guard takes place in winter. The central building, topped with a clock tower, is pierced by three arches which open onto the immense square of Horse Guards Parade where the Changing of the Guard takes place in summer. This is also where the Trooping of the Colour is held to mark the Queen's official birthday.