The Forte de São João da Cadaveira is located on the beach of São João do Estoril and, according to an inscription on the portal of this fortress, its construction began in April 1642 and finished the following year. It is part of the set of Joanine fortresses built between 1642 and 1648 in order to create a defensive line between São Julião da Barra and Cabo da Roca.
The original fortress, protected by a wall of trenches, was reinforced with an exterior wall at the end of the 17th century, and with three sentry houses in three of its angles in the 18th century. It presents square planimetry, divided into two rectangular spaces, corresponding to the battery with a parapet and all accommodation, surmounted by a terrace, following the same type of other fortifications on the coast of Cascais being built at that time. The primitive structural features of the Johannine building remained in spite of some subsequent alterations.
The fortress was decommissioned in 1843, having since served other purposes. At present, this fortress is empty.
Its privileged location, the proximity to Lisbon and Cascais, good roads and pedestrian access constitute an added value for the development of a tourist project in this property.