Barcelos, formerly Mariuá, is a municipality located in the state of Amazonas, northern Brazil. Its population was 27,638 and its area is …Barcelos, formerly Mariuá, is a municipality located in the state of Amazonas, northern Brazil. Its population was 27,638 and its area is 122,476 square kilometres. It is the second largest municipality in Brazil ; equivalent in size to New York state in the United States and slightly larger than North Korea.