The Primera División is the highest level of club football in Argentina. It was founded in 1891 as an amateur competition, becoming professional in 1931 with a league by 18 teams which were dissatisfied with the amateur system they were participating on until 1930. This group of 18 founding members of the present league included nearly all of the most prominent clubs of those times, unified by the idea that full and compulsory amateurism was no longer sustainable (many of those teams are still today among the most popular clubs in Argentina). For many years, the only winners were the so-called "big five" (Boca Juniors, Independiente, Racing Club, River Plate and San Lorenzo de Almagro). This dominance was finally broken in 1967 by Estudiantes de La Plata. Since then, ten other teams have won the championship, resulting in a total of 28 teams having been champions of Argentina as of 2019. River Plate has won the most championships with 36. The only teams outside the Buenos Aires and Greater Buenos Aires to have won the championship are Rosario Central and Newell's Old Boys from Rosario, Estudiantes and Gimnasia y Esgrima from La Plata.