The Castle of Campo Maior (Portuguese: Castelo de Campo Maior) is a medieval military fortification, in the civil parish of São João Bapista, municipality of Campo Maior, part of a first line of defense in the Portuguese Alentejo, oriented towards Spain, in conjunction with the military forts of Ouguela, Elvas, Olivença and Juromenha. It is a walled bulwark of the modern era, highlighted by a Renaissance-era window in the northern tower of the castle.