Complex sentence: It was a privilege reserved only for the local Hidalgos of the oldest mountainous districts of the County of Castile at the time of its foundation, who could ask for or be asked by the Crown for its service at any time.
Split into simpler sentences: It was a privilege reserved only for the local Hidalgos of the oldest mountainous districts of the County of Castile at the time of its foundation. These hidalgos could ask for or be asked by the Crown for its service at any time.