The Brazilian metropolis of Rio de Janeiro was founded on this day by the Portuguese. But, before the founding of Rio, the French already lived on a nearby island.
On this day the Portuguese navigator Estácio de Sá founded the city of São Sebastião do Rio de Janeiro (St. Sebastian on January River). The name Rio de Janeiro (January River) was a former name of the bay on which Rio lies today. Namely, that bay was discovered in January 1502 (hence its name), and was thought to represent the mouth of a great river (which later turned out not to be true).
Interestingly, when coming into the bay, the Portuguese found that the French had already established a colony on one of the islands. And not just any French, but Huguenots (Calvinist Protestants). In fact, at that time, France was religiously divided into Catholics and Huguenots, between which bloody religious wars soon broke out (one episode of this was the infamous St. Bartholomew’s Day massacre).
The Catholic Portuguese entered into a conflict with the nearby Huguenots, who were considered heretics, and managed to drive them out of the bay after two years of bloody fighting. Otherwise, the bay is a good natural shelter and comprises an area of about 412 square kilometers.