The site was chosen on top of the South Essex south ridge, overlooking the Thames estuary, formed from generally soft deposits of London clay. In the 13th century, marshlands would have stretched away to the south of the castle, with the tide occasionally reaching up as far as the base of the hill itself, and the area would have been more wooded than today. By 1235 the park of Hadleigh had been formed around the castle, including woodland, a fishpond, stables and a park lodge, but the castle was also associated with a wider estate including Rayleigh, Thundersley and Eastwood Parks.