s ▁reign ▁in ▁v icious ▁street ▁batt les . ▁ ▁In ▁ 2 7 1 , ▁A ure li an ▁sa iled ▁east ▁to ▁destroy ▁the ▁power ▁of ▁Pal my ra , ▁Sy ria , ▁with ▁a ▁force ▁of ▁leg ion ary ▁det ach ments , ▁Pra et or ian ▁coh ort s , ▁and ▁other ▁caval ry ▁units , ▁and ▁easily ▁defeated ▁the ▁Pal my ren es . ▁This ▁led ▁to ▁the ▁orth odox ▁view ▁that ▁Dioc let ian ▁and ▁his ▁colle agues ▁evol ved ▁the ▁sac er ▁com it atus ▁( the ▁field ▁esc ort ▁of ▁the ▁em per ors ). ▁The ▁sac er ▁com it atus ▁included ▁field ▁units ▁that ▁used ▁a ▁selection ▁process ▁and ▁command ▁structure ▁mode led ▁after ▁the ▁old ▁Pra et or ian ▁coh ort s , ▁but ▁it ▁was ▁not ▁of ▁uniform ▁composition ▁and ▁was ▁much ▁larger ▁than ▁a ▁Pra et or ian ▁coh ort . ▁ ▁Organ ization ▁ ▁Le ad ership ▁▁ ▁Starting ▁in ▁the ▁year ▁ 2 ▁BC , ▁the ▁Pra et or ian ▁pre fect ▁was ▁the ▁command ing ▁officer ▁of ▁the ▁Pra et or ian ▁Guard ▁( pre viously ▁each ▁coh ort ▁was ▁independent ▁and ▁under ▁the ▁orders ▁of ▁a ▁trib une ▁of ▁e quest rian ▁rank ). ▁This ▁role ▁( ch ief ▁of ▁all ▁troops ▁station ed ▁in ▁Rome ), ▁was ▁in ▁practice ▁a ▁key ▁position ▁of ▁the ▁Roman ▁polity . ▁ ▁From ▁V esp as ian ▁on wards ▁the ▁Pra et or ian ▁pre fect ure ▁was ▁always ▁held