More than 2,500 delegates, including the notorious Revolutionary Armed Forces of Colombia, the Mexican Zapatistas, the guerrilla group championing Indian rights, and the Black Panthers are gathering in Brazil for the five-day conference of revolutionaries, called the "Humanities against Neo-Liberalism" summit.
Manoel Lima Amarel, event co-ordinator, said: "We are very pleased that so many minority groups are joining together in Brazil to discuss their causes. It is important for all oppressed Americans to support each other and to work as one."
Conference organisers chose the city of Belem - situated on the banks of the Amazon - because of its historical significance. In 1835, it was the site of a failed uprising by native Indians who were protesting against the slave trade."Having this conference in Belem reminds us how little has changed in the past 160 years," said Mr Amarel.
Despite the presence of known paramilitary groups, the Belem civil police have not objected to the gathering, although they will be listening out for "inflammatory talk".
Conference organisers have banned delegates from exchanging techniques on guerrilla warfare. Mr Amarel said: "This summit is not about violence It's about ideology. There are other ways to destroy the chains of capitalism without resorting to aggression."