The Cordao do Bola Preta parade is famous for attracting a diverse crowd, spanning all ages.
For the first time in its 93-year history, the event allowed electric sound systems and reversed its normal route.
Police said that despite the large crowds, the event had been peaceful.
Dressed as the cartoon character Asterix, Elson de Deus, 65, told Brazilian newspaper O Globo he had been attending the parade ever since he was 13.
This year, Elson de Deus had taken his son along to the parade to continue the family tradition.
Elizete Vieira, 77, said she had waited for four hours to secure her spot in the parade.
Denisa Chagas told the AFP news agency she liked the Bola Preta parade because it “brings everybody together, people from all districts and neighbouring towns”.
Reflecting the name of Bola Preta, or Black Dot, many revelers wore clothes with black polka dots on a white background.
Others dressed as their sports heroes or donned wigs and tutus.
Police said they had detained 15 people for urinating in the street, but that there had been no serious incidents.
Some 400 street parties have been scheduled for the Rio carnival, but organizers say the Bola Preta parade, which dates back to 1918, is the most traditional.
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