Castelo de Monforte, also referred to as Castelo de Monforte de Rio Livre, in Trás-os-Montes, is located in Águas Frias parish, Monforte village, Chaves municipality, Vila Real district, in Portugal.

Monforte de Rio Livre came into Portuguese territory as soon as nationality was established. The oldest reference to the medieval castle goes back to the 12th century, in a document that mentions a noble lieutenant (tenens) from the castle. The Rio Livre court was instituted in 1267. In 1273, the village received a charter from D. Afonso III (1248-1279), when the renovation works of the complex must have started, which, for the most part, has reached the present day. . This sovereign raised the village to the head of territory, within the same process of organization of the northern border that gave rise, for example, to the Castle of Montalegre. It also institutes a two-day fair.