General view of the Sambodrome when the Unidos de Vila Isabel samba school parades during Rio de Janeiro's annual carnival(AFP/Vanderlei Almeida)

Brazil—One of the world’s largest parties, Carnival, is in full swing in Brazil.

Tens of thousands of revelers - and spectators - have descended on Rio de Janeiro, the heart of Carnival festivities. Carnival is a joyful time celebrated in many predominately Roman Catholic countries that precedes Lent, the somber Christian observance leading up to Easter.

The sounds of samba drums and street parades have filled the streets of several Brazilian cities since Carnival officially opened Friday.

The largest parades come Tuesday, when dozens of the country’s top parade groups send elaborately costumed - or virtually naked - dancers and musicians to perform at Rio’s “Sabrodomo.”

Organized by Brazil’s Samba schools, the groups spend all year preparing and rehearsing for Carnival.

Officials in Rio de Janeiro also spend all year organizing the celebration, which ends in the early hours of Ash Wednesday, the start of Lent. This year’s Carnival is expected to draw about 770,000 people. In the United States, New Orleans’ “Mardi Gras” celebration draws thousands every year.