The Campeonato Brasileiro Série A, popularly known as the Brasileirão, is a professional football league at the top of the Brazilian football league system held annually since 1959. Contested by twenty clubs, it operates a system of promotion and relegation with the Série B. The season runs from May to December of the same year, with teams playing 38 matches each, totalling 380 matches in the season. Due to sponsorship reasons, the league is known as the Brasileirão Petrobras.Due to historical peculiarities and the large geographical size of the country, Brazil has a relatively short history of nation-wide football competitions. The modern Campeonato Brasileiro only started in 1971, supported by the military regime of the time and made easier by the advancements in civil aviation and air transport. Before the establishment of a national league the most prestigious football competitions in Brazil were the state leagues, notably the Campeonato Paulista and Campeonato Carioca state championships (the tournaments of São Paulo and Rio de Janeiro states). Most state competitions have a much longer history than the national competition and, consequently, the various state leagues were considered more prestigious than the national league during the first years.