ALES and TERRALBA, DIOCESE of. - In Sardinia; suffragan of Oristano from the second half of the 6th century. The first see was Usellis, whose date of foundation remains uncertain (5th-6th cent.); after it was destroyed by an earthquake, it was transferred to A. (c. 1182). In 1503 it was united « aeque principaliter » to that of T., the earliest documented record of which dates from the 10th century.
The diocese has 44 parishes, 2 chaplaincies, 78 priests, and 85,000 inhabitants, all Catholic.
The diocese of T. had two abbeys: that of S. Tommaso di Tarcidano (now Arcidano) and that of S. Michele di Thamis, both apparently dating from the end of the 11th century. The latter, which belonged to the Vallombrosians, was united to the archdiocese of Oristano in 1803; nothing is known of the former. At Gavinomonreale the Franciscan convent, founded in 1580, still survives; the Capuchins were at Tuili (1646-1884); Villacidro housed the Mercedarians from 1680; the Carmelites had existed at Mogoro since the 14th century.
As for Christian art, noteworthy is the parish church of T., in Gothic-Aragonese style, with a portal and rose windows of noble architecture. The cathedral of A. is a national monument; it also possesses a Baroque silver frontal, a Gothic silver reliquary, and two Renaissance-style chests.