Well, what he stated is roughly
Pre-Marian = Roman Republic Army
Post-Marian = Imperial Roman Army.
So called Marian reformation was said to be done in 108 BC (though today it was accepted to occur more gradually). It was to constitute the land/economic/social reformation that had been plaguing Rome for centuries. simply, poor became poorer, rich became richer and there was very few middle class people who was the source of Roman Legions.
Marius abolished the practice and established professional army who was paid, equipped by state. You should note that they were mostly from urban poor, or Capito Censi (I'm not sure spelling), who was considered as too poor to equip themselves.
Other effect was, through clientale system, army became more loyal to the general, rather than Rome (and Senate)
Other changes around this time were:
Abolishment of classes in main infantry rank (no more Hastatii, Principes, Triarii, that were divided by age group).
More or less uniform equipments through all ranks.
Adoption of Eagle as the Legionery Standard (no more Wolf, Ox, Boar, Minotaur standards, though it seems they were carried somehow).
Obsolation of Manipul tactics and adaptation of Cohort as a battle unit.
