With whimsical floats, thundering drum sections and legions of performers dripping in sequins and feathers, 12 samba schools will compete for the coveted title of carnival champions across two nights of epic booty-shaking.
Flying the colors of their favorite schools -- the pink and green of Mangueira, the blue and white of Portela, the red, white and green of Grande Rio -- some 70,000 spectators will cheer them on from the packed stands of the Sambadrome stadium, the city's designated parade venue, with millions more expected to watch live on TV.
But there is more to carnival than all-night partying.
The samba schools are rooted in Rio's impoverished favela neighborhoods, and each parade tells a story, often dealing with politics, social issues and history.
"The samba schools are tuned in to the social and political scene, and they use their space, that hour on the avenue, to talk about those issues," Vivian Pereira, a member of independent research group Quilombo do Samba, told AFP.
This year's parades include homages to little-known heroes of Afro-Brazilian history, a tribute to multi-platinum samba singer Alcione and a celebration of the Yanomami Indigenous people, who have been ravaged by a humanitarian crisis blamed on illegal gold mining in the Amazon rainforest.
- From Bolsonaro to Lula -
The parades were particularly political under far-right ex-president Jair Bolsonaro, who faced accusations of authoritarianism, racism, environmental destruction and disastrous mishandling of Covid-19 -- all fodder for the samba schools during his presidency (2019-2022).
This year, carnival is hitting its peak just as Bolsonaro, no fan of the festival, is caught up in a damaging police investigation into accusations he and his allies plotted a "coup" to keep him in power despite losing Brazil's 2022 elections.
The overall tone of carnival is less politically charged since veteran leftist Luiz Inacio Lula da Silva returned to the presidency in January 2023.
Invented a century ago by the descendants of African slaves, samba is one of the great symbols of Brazilian popular culture, and of Rio.
Each samba school has 60 to 70 minutes to dazzle its way down the 700 meters (yards) of the Marques de Sapucai, the avenue through the concrete carnival parade temple designed by modernist architect Oscar Niemeyer.
A jury will judge each school down to the minutest detail, with potentially devastating fractions of points deducted for being out of sync, running overtime or lacking flair.
Carnival is also big business for Rio: the party is expected to generate 5.3 billion reais (more than $1 billion) in revenues this year.
- 'Citizenship of fun' -
With some districts of Rio suffering an increase in violent crime, the city has deployed thousands of police for carnival, especially around the Sambadrome.
Officials are also worried over an outbreak of mosquito-borne dengue fever that has killed more than 50 people. Staff will be handing out mosquito repellant to the audience.
Although the parade contest is the climax, Rio has in fact been celebrating carnival for weeks with free-for-all street parties known as "blocos."
A colorful crowd of tipsy revelers descended on the iconic beach neighborhood of Ipanema on Saturday for a bloco in tribute to Afro-Brazilian writer Conceicao Evaristo.
Thanking them, Evaristo told newspaper O Globo she sees carnival as a time not just to celebrate but to reflect on Brazil, a country of vast inequality.
"May this moment of joy transform... Brazilians' everyday social, political and economic relations, and may everyone be included, not just in the citizenship of fun, but in the citizenship of equal rights," she said.