A large part of being a soldier was that you had your own land that you could produce enough food to survive and buy equipment go to war. War where you could capture slaves to work your land and and riches to afford more land. The idea of the state providing the means and equipment to send soldiers to war only happened in the later era where men couldn't get land because of the artistocrats owning it all and the state had to outfit them so they could go to war.
This is true for The early and middle republic Rome, but after the Marian Reforms, and especially during the Principate, Rome maintained a state sponsored standing army, with standardized arms.
Of course after the crisis and eventual fall of Rome, it went back the older way
