built on a rocky outcrop into the river estuary, the fort of são bruno (taking its name from a nearby convent) is in the shape of a star around a raised central square. following a mannerist style, it was built with batteries targeted at both the estuary and towards the land, together with rectangular bartizans on the front corners. the entrance to the interior is through a large arched gate, on which was placed the shield of portugal, with the date 1647. it was equipped with cannon in 1649. a military inspection carried out in 1735 reported that the fort was deactivated and all its artillery had been destroyed. it also stated that at least one of the lower batteries had been invaded by sand. some repairs took place in 1751 and the fort seems to have emerged relatively unscathed from the 1755 lisbon earthquake. throughout the 18th century the fort was deactivated on several occasions and was reported on one occasion to be occupied by farmers. however, it was again in operation during the spanish-portuguese war of 1762–1763, being armed with 16 cannon.