Not only is it a church of inestimable value, but it is also a fascinating puzzle: its central cylindrical body from the Byzantine era stands on a pre-existing Roman thermal structure, but it is not yet clear whether it served as a temple or a baptistery. The original location of the entrance is still a mystery. Questions on the interpretation of the name, or rather of the two ways in which it is known, have continued to be asked for several years. What is certain is that the church of Santa Maria di Bubalis, also known as Nostra Signora di Mesumundu, is among the oldest religious buildings on the Island: its first structure dates back to the 6th-7th century. It stands in Siligo, in the locality known as Biddanoa, rich in aquifers and mineral and thermal springs. During the 11th century, it became the property of the monks of the Montecassino Abbey, who modified its layout by adding an apse to the east and another room on the north side. The two new components were added to the ‘wings’ already built to the south and the west.