▁by ▁an ▁e quest rian ▁of ▁the ▁equ es ▁order . ▁( E quest ri ans ▁were ▁tradition ally ▁that ▁class ▁of ▁citizens ▁who ▁could ▁equip ▁themselves ▁to ▁serve ▁in ▁the ▁Roman ▁Army ▁on ▁horse back ). ▁ ▁From ▁the ▁year ▁ 2 ▁BC , ▁the ▁coh ort s ▁were ▁under ▁the ▁control ▁of ▁two ▁pre fect ures ; ▁however ▁coh ort s ▁continued ▁to ▁be ▁organized ▁independently , ▁each ▁commanded ▁by ▁a ▁trib une . ▁Trib unes ▁had ▁as ▁immediate ▁sub ordinates ▁ordinary ▁Cent ur ions , ▁all ▁of ▁equal ▁rank ▁except ▁for ▁the ▁T rec en arius , ▁the ▁first ▁and ▁prime ▁of ▁all ▁cent ur ions ▁of ▁the ▁Pra et or ian ▁C oh ort s , ▁who ▁commanded ▁also ▁the ▁ 3 0 0 ▁spec ulator es , ▁and ▁with ▁the ▁exception ▁of ▁his ▁second , ▁the ▁Prince ▁Cas tr orum . ▁ ▁From ▁the ▁second ▁century ▁the ▁Pra et or ian ▁pre fect ▁o vers aw ▁not ▁only ▁the ▁Pra et or ian ▁C oh ort s ▁but ▁also ▁the ▁rest ▁of ▁the ▁g arrison ▁of ▁Rome , ▁including ▁the ▁C oh ort es ▁urb ana e ▁(" urban ▁coh ort s ") ▁and ▁the ▁equ ites ▁singular es ▁August i , ▁but ▁not ▁the ▁V ig iles ▁coh ort s . ▁ ▁Following ▁the ▁dissol ution ▁of ▁the ▁Pra et or ian ▁C oh ort s ▁by ▁the ▁em peror ▁Const antine ▁after ▁he ▁defeated ▁them ▁at ▁the ▁Battle ▁of ▁the ▁Mil v ian ▁Bridge ▁in ▁