What number system did the Romans use in complex calculations?

One look at any mathematical formula in Roman numerals is enough to realize that to use this system for anything complex would be extremely difficult, if not impossible. It takes forever to simply right down most numbers! The truth is, the Romans were not overly patriotic when it came to number systems. All the feats of engineering, temples, arenas and palaces would have never become a reality were it not for the ample use of Greek numerals! Roman engineers and scientists were usually either Greeks or Greek-educated Romans (sometimes completely bilingual). The Greek system was much more versatile, compact and well suited for any calculations known to Ancient mathematicians.