How would you make/produce sulfuric acid with tools only the romans had?
There are several naturally occurring sulfate minerals such as copper(II) sulfate (pentahydrate mineral name: chalcanthite) that will decompose into $\ce{SO3}$ when heated to a few hundred degrees, which produces sulfuric acid when dissolved in water.
These compounds were known as vitriols due to their glassy appearance and sulfuric acid was known as oil or spirit of vitriol since it was derived from these minerals.
Chalcanthite seems to be a natural oxidation product of copper deposits.
Copper(II) sulfate in particular was known as Roman vitriol, but I don't know if this means that that was the primary source for the Romans.

In any case, ancient civilizations did not have any means of mass producing sulfuric acid and industrialized processes involving sulfur dioxide from the combustion of elemental sulfur arose much later.