An optio was the second-in-command of a century, after the centurion. Normaly he was nominated by the centurion (optio, in latin, from “optare”, to choose), but sometimes he was choosen by his fellow soldiers. Optiones (plural) were vital in the Roman army. An optio was stationed at the rear of the ranks to keep the troops in order. Their duties would include enforcing the orders of the centurion, supervising his subordinates, and a variety of other administrative duties.
Unlike the centurion, the cuirass was not the distinguishing part of the optio’s uniform. The identifying part would be his helmet; this would have had plumes of horse hair or feathers on either side of his helmet that could be accompanied by a helmet crest. An optio’s armour would be more like those of the common legionary. He could wear the lorica segmentata or a lorica hamata as well as have his gladius on the right, not the left, side. One thing that did separate him from the common legionary was the staff (called a hastile), which was used to keep the legionaries in line. This staff would be roughly as tall as the optio himself. Optiones often carried wax tablets on which they kept the orders of the day.
According to Vegetius, “The Optiones are subaltern officers, so denominated from their being selected by the option of their superior officers, to do their duty as their substitutes or lieutenants in case of sickness or other accident” An optio would usually be expected to take over from the centurion, if the centurion was killed or incapacitated, but this did not necessarily mean that the optio would be promoted to the rank of centurion.
Optio pay was double the standard legionary pay and they were the most likely men to replace the centurion if the position became vacant.
An optio who was being groomed for a position as centurion was known as an optio ad spem ordinis or optio candidatus.
The type of optio most often mentioned was the optio centuriae, who was second in command of a century. However, there were many other administrative and supervisory roles in the legio carried out by a soldier with the title of optio :-
“Optio tribuni”: asisstant of the “tribunus militum”.
“Optio equitum”: the second in charge (after a “decurio”) of a “turma” (30 horse riders).
“Optio speculatorum”: in charge of the “speculators” (explorers and later on, spys).
“Optio stratorum”: in charge of the “stratores”, legionaries acting as military police.
“Optio custodiarium”: in charge of the guard posts of the camp. An officer of the watch.
“Optio valetudinarii”: in charge of the premises of the “valetudinarium”, military hospital.
“Optio fabricae”: in charge of the armoury workshop (repairing or making weapons).
“Optio ad carcerem”: in charge of the prison cells of the “castra legionis”. Carceres in the cities, including Rome, were also under the command of optiones. It seems likely that the carceres in Rome were under the control of optiones attached to the urban cohort.
The funerary stele of the picture was found in Britannia and it belongs to Cacilius, an “optio agricola” (agricultural) of the legio XX Valeria Victrix. Also we can see a real representation of how he would look like.
Optiones vigilum
The vigiles urbani were not a true military organisation, but they used the same rank system for organisation as the legions. During the 1st century, each cohort had five centuries, responsible for two districts of Rome. By the second century, the size of the cohorts was doubled. Each century would have had an optio. Whilst most men in the vigiles of the first century were slaves or freedmen, the officers were not.
It seems likely that centurions and optiones from the legions were used to keep order, perhaps chosen from those whose age or injuries prevent them from continuing in regular military service, but who are still tough enough for a role in Rome that did not involve extensive marching or fighting.
We know that equestrian officers, like Sejanus’ deputy Macro, started off in the vigiles, before being promoted to the urban cohort and then the praetorian guard. It is also possible that legionaries from the urban cohort or praetorian guard might be promoted to serve as optiones or centurions of the vigiles, as a way of proving they are up to holding those positions in the urban cohorts.
Novels of Colin Hough 