Calah
   one of the most ancient cities of Assyria. "Out of that land he
   [i.e., Nimrod] went forth into Assyria, and built Nineveh,
   Rehoboth-Ir, and Calah, and Resen" (Gen. 10:11, R.V.). Its site
   is now marked probably by the Nimrud ruins on the left bank of
   the Tigris. These cover an area of about 1,000 acres, and are
   second only in size and importance to the mass of ruins opposite
   Mosul. This city was at one time the capital of the empire, and
   was the residence of Sardanapalus and his successors down to the
   time of Sargon, who built a new capital, the modern Khorsabad.
   It has been conjectured that these four cities mentioned in Gen.
   10:11 were afterwards all united into one and called Nineveh
   (q.v.).
   

Calah, favorable; opportunity