I have a difficult, possibly impossible question to ask: How much do historians and archaeologists know about Late Antique Mesopotamia? That is, during the several hundred year period between about 350 CE and 650 CE, what was going on in the area that was now Iraq, and what sorts of sources survive? Do we actually have an surviving literary sources from Sasanian Mesopotamia. Clearly this area was still very economically productive, since the Eastern Roman Empire and the Sasanian Empire spend so much blood and treasure fighting over Mesopotamia in the later 5th and 6th centuries.
These may be good readings, Isabel Toral-Niehoff's Al-Hira, al-Hira was the Late Antique Iraqi capital of the Lakhmid Arabs, and Gustav Rothstein's Die Dynastie Der Lahmiden in Al-Hira, Ein Versuch Zur Arabisch-Persichen Geschichte Zur Zeit Der Sasaniden. Both are in German.
the area that was now Iraq
Speaking of Mesopotamia, it may be interesting to note that Iraq is the Arabic equivalent term for that region. For some reason, it's the only Arabic term that non-Arabs have adapted.