These unassuming holes are some the few surviving reminders of a 12th century Augustinian Priory that once stood inside the grounds of Portchester Castle. The feature, which is integrated into the Roman-built defensive wall, are the garderobe chutes that formed part of a reredorter. This is the name given to the communal toilet in mediaeval monasteries. Waste material simply fell into the water to be carried away by the tide. Such a facility  was regraded as most hygienic in the medieval period.