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Legion: alphabetically

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 Although in the third century, large cavalry units gradually superseded the legions as Rome's most important force, many of them are attested in the fourth and early fifth centuries.

The following table catalogue contains only the legions that served under the early empire. Units in italics were part of the army of the emperor Augustus.

I Adiutrix
VII Claudia
I Germanica
VII Gemina
I Italica
VIII Augusta
I Macriana Liberatrix
VIIII Hispana
I Minervia
X Fretensis
I Parthica
X Gemina
II Adiutrix
XI Claudia
II Augusta
XII Fulminata
II Italica
XIII Gemina
II Parthica
XIV Gemina
II Traiana Fortis
XV Apollinaris
III Augusta
XV Primigenia
III Cyrenaica
XVI Gallica
III Gallica
XVI Flavia Firma
III Italica
XVII
III Parthica XVIII
IIII Macedonica XIX
IIII Flavia Felix XX Valeria Victrix
IIII Scythica XXI Rapax
V Alaudae XXII Deiotariana
V Macedonica XXII Primigenia
VI Ferrata XXX Ulpia Victrix
VI Victrix  

In the fourth century, we hear of other legions, but at that moment, the legions were no longer the backbone of the Roman army. Their names are included in the following table:

I Iulia Alpina
I Noricorum
III Herculia
I Armeniaca
I Pontica
III Isaura
I Flavia Constantia
II Iulia Alpina
IIII Italica
 I Flavia Gallicana
II Armeniaca
IIII Martia
 I Flavia Martis
II Brittannica
IIII Parthica
I Flavia Pacis
II Flavia Constantia
V Iovia
I Illyricorum
II Flavia Virtutis
V Parthica
I Iovia
II Herculia
VI Gallicana
I Isaura Sagitaria
II Isaura
VI Herculia
I Iulia Alpina
III Iulia Alpina
VI Hispana
I Martia
III Diocletiana
VI Parthica
I Maximiana
III Flavia Salutis
XII Victrix