[3] The nobility title was used for centuries by the eldest sons of the holders of the marquisate of Aguilar de Campoo, first class Grandee of Spain, nowadays, both dignities are separated.

King Alfonso XI (1312–1350) granted the lordship, together with the territory of Liébana and Aguilar de Campoo (1339), to one of his bastards, the Infante Don Tello Count of Vizcaya and Aguilar, brother of King Enrique II, his son Juan Téllez who married Leonor de la Vega.

Juan Téllez was the heir of Don Tello, Count of Vizcaya, Lord of Aguilar and Castañeda, legitimised son of Alfonso XI.

King Henry II of Castile, in the 14th century, confirmed Castañeda to his brother Tello Alfonso, Lord of Biscay.

[2][3] Shortly before his death in 1370, Tello wrote in his will that Castañeda was to go to an illegitimate daughter named María, who had not been raised with him and who later married Juan Hurtado de Mendoza.

The former because she wanted to keep what she had inherited from her father, and Doña Leonor because once married to Diego Hurtado de Mendoza she wanted to keep her interests in Liébana, Campoo and the Asturias de Santillana intact, which led to serious conflicts between the two houses, the Manrique Counts of Castañeda and future Marquises of Aguilar and the Mendoza family, future Marquises of Santillana, for the possession of the latter territories.

This same loss of land occurred at the same time in other nearby lordships, such as the Marquisate of Aguilar, from which Liébana and La Pernía were separated.

[2][6] The king forbade his lordship and ordered the inhabitants to seize Fernández Manrique if he tried to impose himself on them as lord, and to send him to his court.

He stayed in Aguilar de Campoo and sent ahead the corregidor Pedro González del Castillo with a large escort.

[2] The first count tried to seize the valley of Toranzo and some territories of the Asturias de Santillana, usurping the jurisdiction of the justice in Cartes.

He was heir to Garci Manrique, who left him the county, along with other lands, in his will of 1436,[8] and great-grandson of Tello, brother Henry II of Castile through his mother.

Juan Manrique, who died at the age of 95, left Castañeda to his son Garci Fernández Manrique, who managed to legitimise his possession of Aguilar, as the Catholic Monarchs officially recognised his title of 1st Marquis over that lordship[8] and allowed him to appoint merinos in Trasmiera, Toranzo and Carrión; however, the kings took the opportunity to curtail the rights that the Counts of Castañeda had taken by force in royal territories.