An almost impregnable fortress on the Russo-Turkish frontier in Asia, 100 m. E. of the Caspian Sea; was successfully held by the Turks under General Williams in 1855, of which Laurence Oliphant wrote an account, but captured by Russia in 1877, and ceded to her by the Treaty of Berlin, 1878; it is a strong place, and a prize to any power that possesses it.