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
Mesopotamia used throughout the Greek Septuagint (c. 250 BC) to translate the Hebrew and Aramaic equivalent "Naharaim". An even earlier Greek usage of the name "Mesopotamia" is evident from "The Anabasis of Alexander", which was written in the late 2nd century AD, but specifically refers to sources from the time of Alexander the Great. In the "Anabasis", Mesopotamia was used to designate the land east of the Euphrates in north Syria. The Aramaic term "biritum/birit narim" corresponded to a similar geographical concept. Later, the term Mesopotamia was more generally applied to all the lands between the Euphrates and the Tigris, thereby