At his death in battle in 1143, the castle passed by his will to his son Alfonso Munio, who, as territorial or local surnames were then coming into vogue in place of the simple patronymic, took the additional name of Cervatos.

His eldest son Pedro succeeded him in the possession of the castle, and followed his example in adopting the name, an assumption at which the younger son, Gonzalo, seems to have taken umbrage.
Everyone who has paid even a flying visit to Toledo will remember the ruined castle that crowns the hill above the spot where the bridge of Alcantara spans the gorge of the Tagus, and with its broken outline and crumbling walls makes such an admirable pendant to the square solid Alcazar towering over the city roofs on the opposite side.

It was built, or as some say restored, by Alfonso VI shortly after his occupation of Toledo in 1085, and called by him San Servando after a Spanish martyr, a name subsequently modified into San Servan (in which form it appears in the "Poem of the Cid"), San Servantes, and San Cervantes: with regard to which last the "Handbook for Spain" warns its readers against the supposition that it has anything to do with the author of "Don Quixote." Ford, as all know who have taken him for a companion and counsellor on the roads of Spain, is seldom wrong in matters of literature or history.
In this instance, however, he is in error.

It has everything to do with the author of "Don Quixote," for it is in fact these old walls that have given to Spain the name she is proudest of to-day.

Gonzalo, above mentioned, it may be readily conceived, did not relish the appropriation by his brother of a name to which he himself had an equal right, for though nominally taken from the castle, it was in reality derived from the ancient territorial possession of the family, and as a set-off, and to distinguish himself (diferenciarse) from his brother, he took as a surname the name of the castle on the bank of the Tagus, in the building of which, according to a family tradition, his great-grandfather had a share.
Both brothers founded families.