They bartered using commodities, goods, and pieces of rare metals (gold, silver and copper in particular- which are really just commodities).
Kefirah. The Torah defines money (as per the Gemorah Kiddushin) as a certain value of silver (or gold, as per the Machlokes in HaZahav). That is “Money”, and FRNs, NIS or Wampum is not.
Period.