in 1565 the rio de janeiro region was under the control of the french - when the portuguese wanted to reconquer their former territory, they had to do it with the help of the local indigenous tribes.

araribóia (in tupi language 'cobra of the water') was head of the indigenous tribes who helped the portuguese defeat the french after a ferocious battle on flamengo beach. 

following that victory, estácio de sá formally founded the city of rio de janeiro and rewarded araribóia by letting him have any land he wanted.