The Cathedral of Santa Chiara was the first cathedral in the world dedicated to Chiara of Assisi and is located in the historic center of Iglesias, in Piazza Municipio. It was erected by the will of Count Ugolino della Gherardesca in Roman-Gothic style between 1284 and 1288, and only later, in 1503, did it assume the role of cathedral.
The facade is flanked by a squared bell tower in whose bell chamber there are four bronzeworks, the oldest of which dates back to 1327, by Andrea Pisano.
The interior, extensively renovated starting from the 16th century, has a Latin cross plan with a single aisle and side chapels. The aisle is divided into four bays by pointed arches. The bays were built between 1576 and 1588 and are particularly important for their depictions which refer to the artistic and religious sensibility that characterized the city during the Spanish era.
The crucifix is carved in the first bay, while the second depicts a scene of the martyrdom of Saint Antioco (Patron Saint of the Diocese). The third bay has the figure of Saint Antioco praying in the center. The presbytery vault in the center features Christ in the robes of the Judge at the end of time, while in the minor keystones, Saint Chiara, Saint Sebastian, Saint Antioco, and Saint Giovanni Evangelista (John the Apostle) are depicted.
The altar of St. Antioco is made of carved and gilded juniper wood between 1712 and 1718.