The marquis Malaspina, originally from Lunigiana, an area between Tuscany and Liguria, arrived in Bosa in the 12th century and immediately set about building a fortress to defend the city from frequent Saracen pirate incursions. The castle, which passed into the hands of the district of Arborea in the 14th century, underwent a series of refurbishments until finally expanding to reach 300m in perimeter and is defended by seven towers. The perimeter wall, which offers a splendid view of Bosa, also encloses the Church of Our Lady of Sos Regnos Altos with its precious series of frescoes dating back to the mid-14th century.