County of Trastámara

The County of Trastámara (Spanish Condado de Trastámara) was a tenancy of the crown in the Kingdom of Galicia in the Middle Ages. Its name comes from the Latin tra(n)s Tamar(is), meaning "beyond [north of] the Tambre", a river which runs through Galicia. It was regularly granted to men of a single family, the House of Traba from the 11th century into the 13th, after which it was often given for life to others, including Alvar Núñez Osorio and the future King Henry II of Castile, whose dynasty is thus known as the House of Trastámara. On 4 February 1445 in San Martín de Valdeiglesias, it was granted as a hereditary possession to Pedro Álvarez Osorio by Juan II of Castile.

The river Tambre, southern boundary of the Trastámara