How did trade and barter systems work before money?

The answer

Before formal monetary systems, human societies used diverse exchange mechanisms. Pure barter (direct exchange of goods) was actually less common than anthropologists once assumed; many pre-monetary societies relied instead on gift economies, debt systems, and social obligation networks. When standardized mediums of exchange emerged, they took wildly diverse forms: cowrie shells served as currency across Africa, South Asia, and East Asia for over 3,000 years. The Yap islanders of Micronesia used rai stones, limestone discs up to 3.6 meters in diameter, whose ownership could transfer without physically moving them. Salt was so valuable as currency in ancient Rome that soldiers were paid with it (the origin of 'salary'). Cocoa beans served as currency in Mesoamerica, and tea bricks functioned as money across Central Asia. The first known coins were minted in Lydia (modern Turkey) around 600 BCE, but China independently developed metal coinage around the same period.