TIRGU OCNA (Rumanian also Targul Ocna)  , a

town of Rumania, on the left bank of the river Trotosh, an affluent of the Sereth, and on a branch railway which crosses the Ghimesh Pass into Transylvania . Pop . (1900), 8033 . Tirgu Ocna is built among the Carpathian Mountains, on bare hills formed of rock salt . Outside the town stands the largest prison in Rumania; beyond this are the mines, worked, since 1870, by convicts, who receive a small wage . The thickness of the salt is unknown; the mines yield about 11,000 tons annually .