"It has recently been proved by neutron activation analysis that this attractive pottery was manufactured in large quantities in certain specialized centers, such as Arpachiyah, Tell Brak, Chagar Bazar and Tell Halaf, and exported to specific settlements from which it gradually reached more distant places. The people who transported this ware (perhaps on the back of cattle or on ox-drawn sledges) presumably returned loaded with such 'luxury' goods as marine shells, gem stones and particularly obsidian, which is predominant in most Halafian sites."

Georges Roux, Ancient Iraq, p. 58

(Citation for "Between the Rivers, Before the State.")