It is "one of the few Brazilian fortifications to retain its original appearance from the late 16th century."

[3][4] The Fort of Monserrate was built as early as the Governor-General Manoel Teles Barreto, between 1583 and 1587; and 1609, when it appears in a report by Diogo de Campos Moreno.

It was one of four recorded forts of the period, which included the Towers of Saint Albert (Torres de Santo Alberto), now lost; the Tower of Saint James (Torres de Santiago) in Água de Meninos, now modified into a stronghold; and the second version of the Forte de Santo Antônio da Barra.

[4] The Fort of Monserrate is an irregular polygon-shaped structure, with circular turrets at angles covered by domes.

The fort once had a drawbridge between the ramp and embankment; two barracks once flanked the entrance.