 A new versatile type of unit, the "cohortes equitatae", combining cavalry and legionaries in a single formation could be stationed at garrisons or outposts, could fight on their own as balanced small forces or could combine with other similar units as a larger legion-sized force.This increase in organizational flexibility over time helped ensure the long-term success of Roman military forces.The Emperor Gallienus (253–268 AD) began a reorganization that created the final military structure of the late Empire.