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Also known as the New Castle of Manzanares el Real, it is an important example of Castilian military architecture from the 15th century. Its works began in 1475 and it is built on a Romanesque-Mudejar hermitage. It is one of the best preserved and best-known Spanish medieval fortresses. It is listed as a Historical-Artistic Monument. It is a palace-fortress located in the municipality of Manzanares el Real (Community of Madrid, Spain), next to the Santillana reservoir and at the foot of the Sierra de Guadarrama.

The lands bordering the upper course of the Manzanares River, very rich in pastures and forests, were the subject of frequent disputes between the different powers that emerged after the Reconquista. The Communities of Villa y Tierra de Segovia and Madrid were involved in different disputes throughout the 13th century, which were resolved in the 14th century by King Juan I of Castile with the donation of the region to his steward, Pedro González de Mendoza.

His eldest son, Diego Hurtado de Mendoza, chief admiral of Castile, is credited with the construction of a first fortress, currently known as the old castle of Manzanares el Real, although it is very likely that this building had an earlier origin. In the last third of the 15th century, the House of Mendoza decided to build a new castle-palace, larger and more luxurious, in accordance with the notable political and economic influence achieved by this family.

The function of a palatial residence with which it was conceived barely lasted a century. With the death in 1566 of Íñigo López de Mendoza y Pimentel, fourth Duke of Infantado, the castle ceased to be inhabited, as economic problems and lawsuits arose between the heirs of the House of Mendoza.

Its premises house a museum of Spanish castles, as well as a collection of tapestries. In 1982, the castle hosted the act of constitution of the Assembly of Parliamentarians of Madrid, in which the drafting of the Statute of Autonomy took place.