The hill of Serravalle is a natural bastion overlooking the fertile Temo river valley, surrounded by pastures and forests, and the medieval historic center of Bosa, which earned recognition as the second most beautiful village in Italy. Bosa developed along the slopes of the hill over two centuries between the thirteenth and fifteenth centuries (in the Sa Costa district). The enduring tactical advantage of its location, which allowed control over the area from the sea to the river and the urban settlement in the valley (Bosa vetus), is one of the factors that suggests the site was used continuously over centuries, if only as a lookout to guard against sudden enemy attacks (Saracens, bandits) or fires. Archaeological excavations confirm the existence of an urban settlement in Roman times, which would later become centered around the early medieval cathedral of San Pietro, located within the ‘bishop’s quarter’ and flanked by a Roman-base tower/bell tower, with an adjacent enclosed cemetery. In the early Middle Ages, the site belonged to the Giudicato of Torres, but by the end of the thirteenth century, it was in the hands of the Malaspina marquises (from Lunigiana) through marriage (1232) and due to the gradual decline of that kingdom.