Oitavos Fort, which is rectangular in layout and sits atop the cliff, was built between 1642 and 1648, following the restoration of Portugal’s independence. It was part of the defensive system for the entrance to the Tejo River. The fort was garrisoned by a small detachment, which had the task of stopping hostile forces from landing between Guincho and Guia. The architectural restoration work was closely guided by a 1796 plan of the fort, to ensure the original features were retained. This project has resulted in the recreation of an authentic 17th Century ambience in many of the rooms.