Fordongianus (Greek: Hydata Hypsitana; Latin: Aquæ Hypsitanæ, Aquae Hypsitanae, and later Forum Trajani or Forum Traiani) is a comune (municipality) in the Province of Oristano in the Italian region Sardinia, located about 90 km northwest of Cagliari and about 25 km northeast of Oristano. As of 31 December 2004, it had a population of 1,037 and an area of 39.4 km². Fordongianus borders the following municipalities: Allai, Busachi, Ghilarza, Ollastra, Paulilatino, Siapiccia, Villanova Truschedu. In antiquity, Fordongianus was called Forum Trajani in honor of Roman emperor Trajan, who is credited with the building of what are now considerable Roman remains, including those of a bridge, and of thermae on a scale of great magnificence (Valéry, Voy. en Sardaigne, vol. ii. c. 35). The city, in the interior of Sardinia, is known from the Itineraries, which place it on the road from Tibula, through the interior of the island, to Othoca. (Itin. Ant. p. 82.) Fordongianus sits on the left bank of the river Tirsi (ancient Thyrsus), about 25 km from Oristano.