the forte são joão (saint john fortress) is located in the urca neighborhood of rio,  overlooking the guanabara bay. it was built by the founder of rio de janeiro, estácio de sá, in 1565 and had land batteries added until forming the fortress complex that it is today. there are four main land batteries - são josé, são martinho, são teodosio, and são diogo.

its initial purpose was to repel attacks by the french who ambitioned to hold a possession in the then colony of brazil and tried to destabilize it with harassing incursions throughout the shore. later it gave rise to the escola militar (military school) one of the most prestigious institutions of military instruction in brazil.