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Legion: chronological

A Roman legion was an infantry unit consisting of  heavily armed soldiers, equiped with shields, armor, helmets, spears and swords. In the early republic, the strength of a legion was about 3,000 men; there were 4,800 legionaries in the days of Julius Caesar; the twenty-five legions that defended the empire during the reign of Augustus counted more than 5,000 soldiers. They were the backbone of the Roman army, supported by auxiliary troops. Although in the third century, large cavalry units gradually superseded the legions as Rome's most important force, many of them are attested in the fourth and early fifth centuries.

Julius Caesar
Julius Caesar
Before Caesar:

Julius Caesar, 58 BCE

Caesar, 57 BCE:

Caesar, 53 BCE:

  • XIV (reconstituted)
  • XV (destroyed 49-48 in Africa)
  • XVI (destroyed 49-48 in Africa)

Caesar, 52 BCE:

Caesar, 49-48 BCE (using consular numbers):

Timeline of legions
Timeline of legions
Pansa, 43 BCE: Mark Antony:
Portrait of Augustus as pontifex maximus
Portrait of Augustus as pontifex maximus
Octavian, 41-40 BCE: Octavian 30 BCE: Battle in Teutoburg Forest:
  • XVII, XVIII, XIX destroyed
Caligula, 39 CE:
Nero
Nero
Nero, 66:

Nero, 68:

Galba, 68:
Vespasian, 70:
Domitian
Domitian
Domitian, 83: War against Decebalus, 92: Trajan, 105: Uncertain date:
Marcus Aurelius, 168:
Septimius Severus
Septimius Severus
Septimius Severus, 197: Heliogabalus, 220: Severus Alexander, 230?
Gordian III, 238?:
Philip the Arab
Philip the Arab
Philip the Arab (244-249)? Valerian, 253: Laelianus (268-269)?

The following units are known from late-ancient sources and are called "legions". In fact, however, they were no longer the elite troops of the Roman empire. The main forces were cavalry units; the legions were the garrisons of the frontier zone.

Probus
Probus
Aurelian (270-275):

Probus (276-282) Before Diocletian: