[mywittyname]

It's pretty likely that architects of the time understood place-based arithmetic and used calculators similar to an abacus, even if society as a whole used Roman numerals. The tools a layman use is sometimes different than what a professional does.

We know that other civilization in the region we adept with arithmetic and geometry. And Rome's straight roads and aqueducts are evidence that their citizens understood the practical applications of such mathematics. So it stands to reason someone in the process understood how to perform arithmetic using a place-based notation. Even if they were only generating calculation tables used by field engineers.

I'm sure people devised clever tools that allowed builders to actually build these structures. Much like a roofer today doesn't need to perform any calculations beyond measurements, because they are taught how to use a speed-square to quickly find the correct angles for cutting rafters.