went forth: Targum of Onkelos says: "he [Nimrod] went forth into Asshur" (i.e. invaded it).
Nineveh. The competitor of Babylon as the capital of Assyria.
the City Rehoboth. better, "the city boulevards", in parenthesis.
Related Commentaries of Genesis 10:11
Genesis 10:11
11 Out of that land went forth Asshur, and builded Nineveh, and the city Rehoboth, and Calah,