I believe this is an old thing which pops up anyway, it's not the EB Marian Reforms. From the EB FAQ sticky:

At least year 172BC, have 6 Latifundia built, hold at least 45 settlements, fight more than 250 battles and have a character that is:

Intelligent/Charismatic/Vigorous
Popularis
Consul or Ex-Consul
Has Influence and Command > 2

OR just conquer 90 settlements.
Antagonist