Or Donji Sou, the capital of the Dolnja Tuzla district, in Bosnia, beautifully situated on the Jala or Julia, a small stream flowing into the Spreca, which joins the Bosna at Doboj, 39 m. W.N.W.; and on a branch railway from Doboj. Pop. (1895) 10,227; almost all, including a permanent colony of gipsies, being Moslems. Dolnja Tuzla is the seat of a district court and an Orthodox bishop; with several churches, many mosques, a hospital, gymnasium and commercial school. Besides large alkali works, it has a vigorous trade in grain, livestock, timber and coal, from the surrounding hills, where there is a colony of Hungarian miners; while the salt springs, owned by the state both at Dolnja, or Lower, and Gornja, or Upper Tuzla, 6 m. E., are without a rival in the Balkan Peninsula.
Dolnja Tuzla was called by the Romans Ad Salinas. Constantine Porphyrogenitus mentions it, in the 10th century, as Salenes; in other medieval documents it appears as Sou, Sow or Soli. Its modern name is derived from the Turkish tuz, " salt." In 1690 the Austrians routed the Turks at Gornja Tuzla, and removed the Franciscan friars, with about 3000 other Roman Catholics, into Slavonia.