Zeno

Hello, I recetly played a map and I saw that the gaia faction had some post-marian legionnaires that attacked me. I even saw them in the scenario builder. Is there a way to get those units in single player at a random map? I thought it would be a technology of some sort, similar to the one that Seleucids have (traditional vs. romanized army), but I just couldn't find it, thanks.