Ancient armies and modern armies are the same in most aspects because their role remains the same. The Only difference are in the military terms and the weapons used.
In the Roman army, the commanding officer of a legion was called the Legate. He was assisted by am
adjutant or deputy called the Camp Prefect, and a staff of six senior administrative officers called Tribunes.
The original function of the Tribunes was to spread the call to arms and to ensure that the citizens rallied to
the Eagles in time to march and fight. Later, the Tribunate became more of a political tenure, a training
ground for young noblemen waiting to go into the consular or civil services. Whenever a Tribune chose to
distinguish himself militarily rather than serve his time administratively and get out, his success was almost
preordained.
There were normally 28 legions in commission at any given time, and each legion was divided into 10
cohorts. By the end of the third century, the first two cohorts of each legion had been expanded to
Millarian status, which meant that each held 1,00 men and was the approximate equivalent of the modern
battalion. Prior to that time, only the First Cohort had been Millarian. To the First and Second Cohorts fell
the honor of holding the right of the legion's line of battle, and they were made up of the finest and
strongest battle-hardened veterans. Cohorts Three through Ten were standard cohorts of 500 to 600 men.
Each Millarian cohort was composed of ten maniples, and a maniple was made up of ten squads of 10
to 12 men each.
The bulk of the legion's command was provided by the Centuriate, from the ranks of which came the
centurions, all the middle-and lower-ranking commissioned officers of the legion. There were six
centurions to each cohort from Three to Ten, making 48, and five senior centurions called primi ordines, in
each of the two Millarian Cohorts. Each legion had a primus pilus, the senior centurion, a kind of super-
charged Regimental Sergeant Major. The primus pilus headed the First Cohort, the Second Cohort was
headed by the princeps secundus, and Cohorts Three through Ten were each commanded by a pilus prior.
The Roman centurion was distinguished by his uniform: his armor was silvered, he wore his sword on
his left side rather than his right, and the crest of his helmet was turned so that it went sideways across his
helmet like a halo.
Each centurion had the right, or the option, to appoint a second-in-command for himself, and these
men, the equivalents of non-commissioned officers, were known for that reason as optios. Other junior
officers were the standard bearers, one of whom, the aquilifer, bore the Eagle of the legion. There was also
a signifer for each century, who bore the unit's identity crest and acted as its banker. Each legion also had a
full complement of physicians and surgeons, veterinarians, quartermasters and clerks, trumpeters, guard
commanders, intelligence officers, torturers and executioners.
The Roman Cavalry
By the end of the second century AD, cavalry was playing an important role in legionary tactics and
represented up to one-fifth of overall forces in many military actions. Nevertheless, until the turn of the fifth
century, the cavalry was the army's weakest link.
The Romans themselves were never great horsemen, and Roman cavalry was seldom truly Roman.
They preferred to leave the cavalry to their allies and subject nations, so that history tells us of the
magnificent German mixed cavalry that Julius Caesar admired, and which
gave raise to cohortes equitates, the mixed cohorts of cavalry and infantry used in the first, second and
third centuries AD. Roman writers also mention with admiration the light horsemen of North Africa, who
rode without bridles.
Fundamentally, with very few exceptions, cavalry was used as light skirmishing troops, mainly
mounted archers whose job was patrol, reconnaissance and the provision of a mobile defensive screen
while the legion was massing in battle array.
Roman cavalry of the early and middle Empire was organized in alae, units of 500 to 1,000 men
divided into squadrons, or turmae, of 30 or 40 horsemen under the command of decurions. We know that
the Romans used a kind of saddle, with four saddle horns for anchoring baggage, but they had no
knowledge of stirrups, although they did use spurs. They also used horseshoes and snaffle bits, and some
of their horses wore armored cataphractus blankets of bronze scales, although there is little evidence that
this form of armor, or armored cavalry, was ever widely used.
Until the fifth century, and the aftermath of the Battle of Adrianople, it would seem that almost no
attempt had been made to study the heavy cavalry techniques used in the second century BC by Philip of
Macedon and his son Alexander the Great. It was that renaissance, allied with the arrival of stirrups in
Europe somewhere in the first half of the fifth century, that changed warfare forever. In terms of military
impact, the significance of the saddle with stirrups was probably greater that the invention of the tank.