Northampton Castle was one of the most famous Norman castles in England. It was built under the stewardship of Simon de Senlis, the first Earl of Northampton, in 1084. It took several years to complete, as there is no mention of it in the Domesday Book, a great survey of England completed in 1086. The castle site was outside the western city gate, and defended on three sides by deep trenches. A branch of the River Nene provided a natural barrier on the western side. The castle had extensive grounds and a large keep. The gates were surrounded by bulwarks made of earth, used to mount artillery.