Birtha (Mesopotamia) bastions are quite traceable. There are the ruins of a vaulted secret staircase, leading down from the heart of the citadel to the water's edge. Birtha (Mesopotamia) Birtha () was an ancient fortress on the river Tigris, which was said to have been built by Alexander the Great. It would seem, from the description of Ammianus, to have resembled a modern fortification, flanked by bastions, and with its approaches defended by out-works. Shapur II here closed his campaign in 360, and was compelled to retire with considerable loss. D'Anville and Edward Gibbon both identify Birtha as modern-day Tikrit, Iraq. The
Geography of Mesopotamia was similarly known as "Gu-gubba" (Akkadian "Kisad tamtim") "bank of the sea." A more comprehensive name of southern Mesopotamia was "Kengi", "the land," or "Kengi Sumer", "the land of Sumer". Sumer has been supposed to be the original of the Biblical Shinar and the Sankhar of the Amarna letters. Opposed to Kengi and Sumer were Urra (Un) and Akkad or northern Babylonia. The original meaning of Urra was perhaps "clayey soil," but it came to signify "the upper country" or "highlands," "kengi" being "the lowlands." In Semitic times, Urra was pronounced Un and confounded with "uru", "city" as a geographical