Dublin has many landmarks and monuments dating back hundreds of years. One of the oldest is Dublin Castle, which was first founded as a major defensive work on the orders of England's King John in 1204, shortly after the Norman invasion of Ireland in 1169, when it was commanded that a castle be built with strong walls and good ditches for the defence of the city, the administration of justice, and the protection of the King's treasure. Largely complete by 1230, the castle was of typical Norman courtyard design, with a central square without a keep, bounded on all sides by tall defensive walls and protected at each corner by a circular tower. Sited to the south-east of Norman Dublin, the castle formed one corner of the outer perimeter of the city, using the River Poddle as a natural means of defence.