Construction of the cathedral began in the second half of the 16th century, following the establishment in 1503 of the Diocese of Alghero. The first phase began in 1567, immediately after the demolition of the old parish church; the radial chapels located behind the chancel and the bell tower with its portal, in Catalan Gothic style, can be attributed to that early period. The building has a nave and two lower side aisles; on the intersection of the arms of the transept stands the octagonal dome on a high windowed drum. The marble complex of the chancel, the pulpit adorned with a relief depicting the preaching of the Baptist, the stoups and the Angel of the baptismal font were executed by Giuseppe Massetti of Genoa between 1723 and 1730. The cathedral features an imposing neoclassical pronaos, designed in 1862 by engineer Michele Dessì Magnetti and set against the old Renaissance facade.
