I'm a little stymied by the following passage from the "Res gestae divi Augusti" in which he claims to have given (out of his own pocket) 150 million sesterces to the treasury. Or at least that is what the translation (from a calendar with some daily Latin) says. I do not understand how the "million" is being expressed. Here's the original passage:
Quater pecunia mea iuvi aerarium, ita ut sestertium milliens et quingentiens ad eos qui praerant aerario detulerim. Et M. Lepido et L. Arruntio cos. in aerarium militare, quod ex consilio meo constitutum est ex quo praemia darentur militibus qui vicena aut plura stipendia emeruissent, HS milliens et septingentiens ex patrimonio meo detuli.
According to my dictionary "milliens" means "a thousand times", and "quingentiens" means "500 times". Put together this ought to mean "1,500 times" instead of "150 million times". Is it simply understood in view of the context that greater sums are meant? Even then, why exactly by a factor of "100,000"?
And what in general was the way of the Romans of the late republic and early empire to express the concept of "million".