The following passage is from a letter written by an Old Assyrian merchant, reporting the expenses incurred along a segment of the trip from Ashur to Kanesh, which hosted a trading colony occupied by Assyrian merchant families resident in Anatolia. At its peak around 1910-1830 B.C.E., the Old Assyrian trade network transported Iranian tin and Babylonian woolen textiles by donkey caravan to Anatolia, where they were sold for silver and gold. This letter and others from the period document the day-to-day mechanics and expenses of running a long-distance-trade business and show that the system for collecting taxes, tolls, and other moneys along the trade route was as highly developed as the trade network itself.

From (the town of) Wahshushana until Shalatuwar we had to pay 0.96 kg of copper each for custom duties as well as for fodder for...