In this first stage of currency, metals were used as symbols to represent value stored in the form of commodities. This formed the basis of trade in the Fertile Crescent for over 1500 years. However, the collapse of the Near Eastern trading system pointed to a flaw: in an era where there was no place that was safe to store value, the value of a circulating medium could only be as sound as the forces that defended that store. A trade could only reach as far as the credibility of that military. By the late Bronze Age, however, a series of treaties had established safe passage for merchants around the Eastern Mediterranean, spreading from Minoan Crete and Mycenae in the northwest to Elam and Bahrain in the southeast. It is not known what was used as a currency for these exchanges, but it is thought that ox-hide shaped ingots of copper, produced in Cyprus, may have functioned as a currency.