The Santa Maria Assunta cathedral was elevated by Pius XII to the rank of minor basilica. The ‘mother’ church of the Arborea archdiocese, the Duomo di Oristano was built on a Paleo-Byzantine structure and atop 6th-7th century Byzantine tombs situated in the parvis of the church. According to tradition, the capital of the Giudicato di Arborea was transferred from Tharros to Oristano in 1070. Documentation from 1131 lists the Ecclesia Sanctae Mariae de Orestano as already being a cathedral. The 16 marble casks housed in the Tridentine Seminary, which overlooks the courtyard of the cathedral in front of the Chiesa della Santissima Trinità (18th-19th century), suggest that the original Romanesque structure of Santa Maria (11th-12th century) had three aisles, with perhaps eight columns on each side dividing the space within. In the first three decades of the 13th century, the church was ‘overhauled’ and in the mid-14th century, the transept was added with four chapels in Gothic-Italian style, including that of the Madonna del Rimedio, today amongst the very few original elements to survive.