The area where the city stands was 'discovered' on the 1st of January 1502 during a Portuguese expedition led by Gaspar de Lemos, who believed he had reached the mouth of a great river, and named the city 'River of January' accordingly.

In 1565 the Portuguese general Estácio de Sá officially founded the city in an attempt to expel the French who had been fighting to take control of the area for 10 years: he named the city 'São Sebastião do Rio de Janeiro,' and until the eighteenth century the city was called just 'São Sebastião.' São Sebastião the First was Portugal's king at the time of the city's creation, march 1st 1565, and he was carrying the same name of the saint that was later made saint patron of the city: São Sebastião.