Rome’s Evolving Army
By Steve Cabral
The Roman Army holds the distinction of being
the longest continually serving force known in military history.
It was designed to defend the city state in her early days
and armed and equipped in the Greek phalanx style common in
the Mediterranean world. The early army is known as the Servian
Army and was a citizen force of all males 17-60 with an age
46 cut-off for non-garrison service. Wealth determined place
in the ranks with the richest going to the cavalry (equites).
Eventually the Equites became the Equestrian Order between
the Plebian (lower) Order and Patrician (Noble) Order.
The bulk of citizens became heavy infantry armed with the
pike (sarissa) and wearing square bronze chest and back plates,
and the poorest became the unarmored skirmishers. The heavy
infantry was organized into three ranks from front to rear:
Hastati (youngest and greenest), Principes (veterans) and
Triarii (oldest veterans and semi-elite). The Rorarii appear
to have been a reserve held with the Triaii, possibly a medium
infantry of older ex-velites. Accensi (Latin: singular) appear
to be a rear rank reserve of servants from the fifth rank
of citizens who fought if things were desperate. Ahead of
the army were Velites, poor citizens who skirmished with javelins
against an advancing force, eventually fading through the
heavy infantry ranks as the main battle was joined. This army
served under the Roman kings from the 6th to the 4th century
BC. Its main opponents were Gauls, Etruscans, Greek colonists,
Campanians, Bruttians and Samnites - all from north or south
The next incarnation of the army was the Camillan army alleged
(but unlikely) to have been established by Fluvius Camillus.
The legions (Latin: Legio) were reorganized into a more compact
organization. The Hastati were given a semi-rectangular shield
and re-armed with the Pila, the heavy long untempered pointed
javelin thrown before contact. The Rorarii and Ascensii both
disappeared from the army. They were still about against Pyrrhus
and gone by the Second Punic War. The success of the Hastati
caused the principes to be rearmed as the hastati (probably
as the hastati aged they became principes with their pilum
retained). The triarius maintained the long spear and wore
chainmail; the velites were unchanged. Cavalry strength was
set at 300 men. The short sword Gladius Hispanicus was adopted
during the Second Punic War.
This army conquered the Mediterranean world from Spain to
Syria. In this period a Roman Legion was paired with an allied
legion, both armed the same. Hirelings from other city states/barbarian
tribes could be engaged to fight in their native way under
their own leadership; Gallic cavalry, Cretan archers and Balearic
slingers were highly prized. After the wars came to an end
the late 2nd century saw a number of disastrous encounters
with Germans crossing into Northern Italy from the Alps. The
Battle of Arausio 105BC saw 80,000 Romans killed in one day
- a bigger defeat than Cannae. With this defeat Gaius Marius
took charge of Rome and altered the army irrevocably.
Rome started as a city-state as in Classical Greece. With
the expulsion of the Tarquin kings in 509BC a Republic was
established. Surrounded by enemies, she slowly expanded her
borders over the centuries until Rome suddenly found herself
an empire ruled by an unwritten constutution that was not
meant to cope with such a large land area. Slavery destroyed
the independent free farmers who formed the backbone of Rome’s
armies and turned them into urban poor who needed a welfare
state to keep them from turning restive. Harsh measures against
non-citizens caused discontent in provinces leading to the
Social War in which Italian city-states rose against Rome
demanding citizenship rather than independence, and also led
to the Spartacus slave revolt. The age of the dictator was
at hand and arose in the late 1st Century under Gaius Marius,
a non-patrician brilliant general who became rich in Spain,
Sulla his patrician subordinate, Sulla’s subordinate
the non-patrician Pompey, and Marius’s patrician nephew
The Senate had to react after its army was destroyed at Arausio.
Rome always found herself with limitless manpower, and Senators
were shocked to find that it was gone. Marius assumed the
consulship and promised the Senate he would have no problem
assembling an army. He then recruited from the Censii (head
count) - the poor of Rome. Idle young men flocked to Marius,
forever giving him and his family (the Caesars) the poor's
votes and loyalty. He reorganized the legions (Legio) into
10 cohorts - nine of 480 men, one of 600 men and a small 120-man
cavalry contingent. Each cohort had six 80-man centuries (the
missing 20 men are believed by some to be the old rorarii
who served as servants and were promoted into the army as
casulties caused openings). The 7th and 9th cohort were the
most junior and the 1st and 6th the most veteran in quality.
The troops were armored in mail as the triarius had been and
all armed with the semi-rectangular shield, bronze helmet,
Gladius Hispanicus and two pila.
At Vercellae, Marius, Sextus Julius Caesar and
Sulla shattered the German army, killing 90,000 to 160,000
combatants and then hitting the German camp taking the woman
and children as slaves. The new Marian army was a success,
but Marius took all of the credit for victory and thus alienated
his two subordinates, eventually starting a string of civil
wars that (except for the Gallic Wars) saw the Marian legions
fight other legions more often than against barbarians and
foreigners. The Marian legion was reformed under Augustus
Caesar after he became Emperor, making it a professional army
with a vastly different Auxilla.
Under Augustus the 10 cohorts and legionary cavalry were
unaltered (except for an improved bronze helmet) until they
received their iron helmets, segmented plate armor and rectangular
shields after 30 AD. Eastern armies of Rome kept chainmail
armor. In many Legions one in four of the men carried slings
and a wedge formation became more common. The Auxilla were
formed into regular combat units. Infantry was organized as
cohorts and equipped with a shield similar to that of the
Camillian legions and with a javelin rather than the specialized
pila. Full cohorts of archers (Sagitarius) were used to replace
the light infantry Cretan archers. Their uniform varied depending
on origin, with Easterners wearing more modest clothing. The
Auxilla cavalry had a hexagonal shield, chainmail (some scale
used especially after Nero) and javelin; a long sword called
a Spatha was eventually adopted. Natives were occassionally
hired on a short-term basis but not as heavily relied upon
as in Marian and earlier armies.
This change caused an evolution in battle tactics, the Auxilla
softened up the enemy force much as the Velites had once done.
Their open order gave them more flexibilty than the Legio
but less staying power. After intense pressure they would
withdraw behind the heavies who would close in for a decision.
Unlike the early Auxilla they were powerful enough to fight
and win on their own as they did versus the Caledonians in
Agricola’s British campaign. Auxillia were paid as regular
troops, served 20 years, and received full citizenship on
discharge. Both Marian and Imperial Legions had artillery
batteries of light bolt throwers and heavier rock throwers.
Staffing of batteries is unclear but probably came from 1st
After 250AD the Imperial Legions deteriorated greatly in
quality. Cavalry became the dominant arm, the infantry began
shedding armor and barbarian hirelings became more important
than ever. After Adrianople in 378AD cavalry would remain
the arm of decision until Swiss pike blocks, English longbows
and early firearms became dominant in the late middle ages
and early modern period.
How will your Roman Army evolve?
at War: Queen of the CeltsTODAY!