A bishop’s seat for three centuries from 1213 - the date of its construction – until 1503, the year in which the diocese transferred to Iglesias. The former cathedral of Tratalias, named after the Catalan-Aragonese period as the Madonna di Monserrat, it sits in the midst of an uninhabited village, the original nucleus of the Sulcian village. A splendid jewel of Romanesque art, it has unique architectural features on the island landscape. Two inscriptions conserved within the building mark the beginning and end (1213 and 1282) of the cathedral’s period of construction. Its history is connected to the events of the Sulci diocese, with the bishop moving to Tratalias after the abandonment of Sant’Antioco due to continuous Saracen invasions.

The Church of Santa Maria maintains a late-Romanesque architectural style that predates the arrival of the Gothic one. It is thirty metres long, thirteen wide and twelve high, made of sedimentary and volcanic stone. The interior has a rectangular layout, divided into three naves with rounded arches set on quadrangularly formed pillars. The apse oriented to the northwest is semi-circular, whilst the roof consists in wooden trusses. The stairs, external and internal, are full of symbolic value, representing an architectural unicum. The light filters in from a number of single-lancet windows on the sides, a rosette on the façade and an open mullioned window above the apse. In the left nave, a retable from 1596 depicting the Madonna enthroned between the Saints John the Baptist and John the Evangelist is to be admired.

The façade is divided into two elements. The lower is tripartite and has smooth lateral panels, decorated only with a lozenge (another original detail). At the centre is the portal, architraved and surmounted by a round arch. The second is surmounted by a tympanum. The façade, side walls and apse are decorated with hanging arches. Somewhat particular are the sculptures on the capitals of the southern portal, hailing from Pisa, and the bas-relief depicting two lions on the architrave of the north portal. A pediment pierced by a cross-shaped light concludes the apse.

The church is to be visited together with the museum of the Tratalias territory, which stands in the same piazza and exhibits images and reconstruction of ancient Tratalias – the former cathedral sits at the centre of what remains of the medieval villa of Tatalia, abandoned in the second half of the 20th century, following infiltrations and subsidence of the land after the formation of the Monte Pranu dam. The town was re-founded not far away. Of the flourishing ancient village, a fundamental town in the Sulcis area throughout the centuries in which it was diocese, remain a number of houses in their original layout, which have today been restructured.