It is a good post that you mentioned that the Roman economy used the tax system and loots through the Roman traditional conquests. In addition to this, I would like to talk about importing and exporting goods during the time period of the Roman Empire that the importing and exporting goods significantly boosted the Roman economy, for example, the Romans bought wheat, livestock lead, woolen products and tin, and they sold wine, olive oil, pottery and papyrus. Therefore, Imports and Exports were very significant to the Roman economy, were the number one key factor, although the tax system circulated the economy.
Rifat