Money was not symbolic in ancient Mesopotamia. What was used as money had a value of its own.
- Paper money is highly symbolic because the paper isn't useful for anything else and it represents a monetary value many, many times the value of the paper and ink.
- Coins don't have to be symbolic, only, but they tend to be. At the moment, in the U.S., oddly, the copper in our pennies is probably worth more than the symbolic value of one cent, but generally coins represent a value that is higher than the sum of their constituent parts.
- Often coins are about as worthless as the paper of paper money, although they have symbolic value used for transactions.
Barter is a form of trade that is (1) not symbolic and (2) where the units of exchange have intrinsic value. The Mesopotamians, who, like most peoples, presumably did barter, also exchanged in non-barter trade, using an odd assortment of money for their transactions.
Marvin A. Powell, in "Money in Mesopotamia," lists the types of money used by people of ancient Mesopotamia from probably the third millennium B.C., by which date Mesopotamia was already part of an extensive trade network [see the silk road]. Money was not in coin form at that time, although words like minas and shekels* -- used in connection with coinage and perhaps familiar from the Bible -- were applied to the weights of the ancient Mesopotamian form of money. For instance:
"The average well to do woman wore golden earrings (sometimes large) and silver rings on the arms and the feet. Those silver rings have a standard weight (5 shekels...) identical with standard fractions of the brideprice, and it is possible that the rings actually represented the price paid."
"Women in Mesopotamia," by M. Stol Journal of the Economic and Social History of the Orient, Vol. 38, No. 2, Women's History (1995), pp. 123-144.
In order from least valuable to most, the money of ancient Mesopotamia was
- lead (especially in northern Mesopotamia [Assyria]),
- copper or bronze,
- "Money in Mesopotamia," Marvin A. Powell. Journal of the Economic and Social History of the Orient, Vol. 39, No. 3 (1996), pp. 224-242.
- "How Interest Rates Were Set, 2500 BC-1000 AD: Máš, tokos and fœnus as Metaphors for Interest Accruals," Michael Hudson. Journal of the Economic and Social History of the Orient, 2000.
- "'Modern' Features in Old Assyrian Trade," Klaas R. Veenhof. Journal of the Economic and Social History of the Orient, Vol. 40, No. 4 (1997), pp. 336-366.
- "Sennacherib's Alleged Half-Shekel Coins," Peter Vargyas. Journal of Near Eastern Studies, Vol. 61, No. 2 (Apr., 2002), pp. 111-115.
Also see: The History of Money.* Online references to the value of (Minas and) Shekels say that 3000 Shekels = 1 Talent in the Bible, but that in Babylonia, 1 Talent = 3600 shekels. I haven't found a source for the Babylonian figure, but Encyclopaedia of the history of science, technology, and medicine in non-western cultures, by Helaine Selin (1997) indicates the basis is the weight of the actual metal.