Long before the concept of money existed, human societies found ways to trade what they had in excess for what they needed. This was the barter system, a method that worked on mutual need. Farmers exchanged grains for tools, shepherds bartered wool for pottery, and communities grew around the rhythm of seasonal and localized trade. Barter worked best in tightly-knit societies where trust was high, but it could not support growing, complex economies that stretched across regions and peoples.