Salamanca (sälämängˈkä) [key], city (1990 pop. 206,275), Guanajuato state, W central Mexico. Chiefly an oil center, it also serves as the commercial and distribution point for the surrounding agricultural region. The city lies on major national highway and rail systems. The first important battle between liberals and conservatives in the 19th-century War of the Reform (see Mexico) was fought at Salamanca.