The São Teodósio da Cadaveira Fort was built in 1643, in order to protect the lisboa region Coast from enemies attacks, and to defend as well the entrance of the Tagus river. The fort has a Mannerist military architecture with a quadrangular plant and the battery facing the ocean.
Of the bulwarks that reinforced the fortress on the ocean side barely nothing exists these days. There are three watchtowers and from the medallion that existed on the top of door, only remains the stone foundation.