The Chronicon Albeldense records the desertion of “castrum...Sigerici” [Castrojeriz] by “Munio filius Nunni” on the arrival of the Muslims in 882. The Chronicon Albeldense records in 883 that the Muslims captured “castellum Sigerici”. ["…Pelagius comes, Froila comes, Lucidius comes, Erus Fredernandi, Ascarius, Petrus, Munio Muniz comes, Osorio comes, Gundesaluus comes…" subscribed the charter dated 6 May 899 under which Alfonso III King of Asturias consecrated the church of Santiago de Compstela. “...Munio Muniz comes...” has not otherwise been identified. He may have been Munio Núñez, although most of the other subscribers can be identified as Galician.].
He is referred to as Conde en Castilla 1 Mar 899, 1 Feb 909 and 23 Jul 909, although he was probably not in control of the whole county. The dating clause of a charter dated 1 Mar 899 records “rex Adefonso in Obieto et comite Munnio Nuniz in Castella et comite Gundissalbo Fernandiz in Uurgos”. He is referred to as father-in-law of García de Asturias in Ximénez de Rada, suspected of preparing a rebellion against King Alfonso III in 910 and placing his son-in-law on the throne. 1
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