It was built in the 17th century, at the same time as the city walls and the San Sebastián castle by the military engineer Juan Villarroel y Prado and the brothers Carlos and Fernando de Grunemberg. There are three parts to it, of which the first and some of the second were made of stone. It was built as a result of the Portuguese War of Succession (1640-1668), in order to protect the city from the English, who were allied with Portugal in the war. The parts made of stone remain today, with the bastions and the sentry boxes.