Legionary+economy

Conquer, plunder, and send stuff to Rome. Triumphs came hand in hand with plunder. Created local economy in a lot of places Rome conquered. Economy followed Roman armies. Prostitution was big industry

Camped out in places, wherever army camped, made locals supply food, form towns. A lot of veterans were given land in places where they had conquered, so had personal interest to improve economy of marchlands. And brought slaves back to Rome.