 As there are very few other sources for this period, most of these names are not certain.Little more of these kings' reigns is known, but Elam seems to have kept up a heavy trade with the Sumerian city-states during this time, importing mainly foods, and exporting cattle, wool, slaves and silver, among other things.A text of the time refers to a shipment of tin to the governor of the Elamite city of Urua, which was committed to work the material and return it in the form of bronze — perhaps indicating a technological edge enjoyed by the Elamites over the Sumerians.