It is a defensive construction of predominantly neoclassical style. In the time of Felipe II. a first castle was built and later renovated between 1731-1775. It served to defend the Ferrol estuary and any possible attacks by land. It is one of the most representative examples of the great fortifications with bastioned batteries of the 18th century. designed with an area of cannon batteries directed to sea complemented by a system of bastions. or protruding walls. which covered the defence of the curtain walls’ flanks (the front walls). These bastions also served to repel attacks by land. Next up are the academic pieces and poliorcetica (literature dedicated to the art of attacking and defending a stronghold) from the age of Enlightenment: the application of mathematics to the art of war. the geometric layout of buildings and the use of factories of quarried stone. The military engineers who designed it were Francisco Montaigú. Juan de la Ferriére and Juan Vergel. Recovered for public use. it has magnificent views over the entire estuary and the Castle of A Palma. which also defended the entrance of the estuary from the other side.