Complex sentence: The Gastein valley had been a part of the Archbishopric of Salzburg in the Middle Ages, it was originally a gold mining area and the site of an ancient trade route crossing the Central Eastern Alps.
Split into simpler sentences: The Gastein valley had been a part of the Archbishopric of Salzburg in the Middle Ages. It was originally a gold mining area and the site of an ancient trade route crossing the Central Eastern Alps.