There are inscriptions that were set up by soldiers following their discharge which give a rough idea, but evidence is severely lacking to make a accurate estimation.

ILS 2302: 120~ men.

CIL III 6580: 120~ men.

CIL III 6178: 100~ men.

CIL III 14507: 230@ men.

Hopkins suggests that the year of service was extended by Augustus in order to actually save money on the discharge bonuses, given that the rate of mortality (estimated at 44%-55% over a 25 year period) increase significantly. As I said however, we do not really have the evidence to provide an accurate figure.

Duncan-Jones, R. (1994). Money and Government in the Roman Empire. Cambridge.

• Page 35 onwards: discusses the cost of discharge bonuses within the imperial budget.

Hopkins, K. (1980). ‘Taxes and Trade in the Roman Empire (200 B.C. – A.D. 400)’. The Journal of Roman Studies Vol. 70: 101-125.