The Pyrenean Mastiff (Spanish: Mastín del Pirineo, Aragonese: Mostín d'o Pireneu) is a large breed of livestock guardian dog from the autonomous community of Aragón in north-eastern Spain. It was traditionally used to protect flocks during the annual transhumance to high summer pasture in the Pyrenees. :552 It is a distinct and separate breed both from the Pyrenean Mountain Dog and from the Pyrenean Shepherd. (2009). Guía de campo de las razas autóctonas españolas (in Spanish). Madrid: Ministerio de Medio Ambiente y Medio Rural y Marino. ISBN 9788449109461.