but the prime position of the island, right before the mouth of the bay and with a good overview over it and the surrounding lands, made the portuguese quickly came to the conclusion that it was a great place to build a fortification.

a fort was indeed built in 1624, and during the following decade this construction would be vastly rebuilt in order to better perform its duty and renamed 'santa margarida da ilha das cobras'.

in the 18th century renewed confrontations with the french would require the construction of two more forts, which would be united and baptized 'fortaleza do patriarca de são josé da ilha das cobras', usually simply known as são josé da fortaleza (san josé of the fortress).