What did Rome use to improve trade, collect taxes, and pay soldiers?

An empire of trade

125 AD. Roman transport in this era was based on sea routes and roads. Trade was made simpler by the use of a single Roman currency.

Tax farmers (Publicani) were used to collect these taxes from the provincials. Rome, in eliminating its own burden for this process, would put the collection of taxes up for auction every few years ... These payments were, in effect, loans to the state and Rome was required to pay interest back to the Publicani.

Roman soldiers were partly paid in salt.