- Many of the Roman Legions were either formed to campaign in the Gallic Wars (58-51 BCE), or to campaign in the Civil Wars (43-31 BCE).
- Although more Legions were added from time to time, the total number on active service during the Empire averaged around 30.
Pompey Consul and Dictator (70-64 BCE)
- 65 BCE Legio VII Claudia
- 65 CE Legio VIII Augusta
- c.48 BCE Legio XXII Deiotariana
Julius Caesar Dictator (49-44 BCE)
Levied to campaign in the Gallic Wars:
- 58 BCE Legio IX Hispana
- 58 BCE Legio X Equestris Later known as the Legio X Gemina
- 58 BCE Legio XI Claudia
- 58 BCE Legio XII Fulminata
- 58 BCE Legio XIV Gemina
- 57 BCE Legio XIII Gemina
- 52 BCE Legio VI Ferrata
- 52 BCE Legio V Alaudae
Levied to campaign in the Great Roman Civil War:
- c.48 BCE Legio I Germanica
- 48 BCE Legio IIII Macedonica
- c.49 BCE Legio III Gallica
Mark Anthony Triumvir (43-33 BCE)
- 43-31 BCE Legio III Cyrenaica
- 42 BCE Legio IIII Scythica
Gaius Vibius Pansa Caetronianus: Consul (43 BCE)
- 43 BCE Legio III Augusta
- 43 BCE Legio V Macedonica
Augustus (27 BCE-14 CE)
- c.43 BCE Legio II Augusta
- 41 BCE Legio VI Victrix
- 41/40 BCE Legio X Fretensis
- 41/40 BCE Legio XV Apollinaris
- 41/40 BCE Legio XVI Gallica
- c. 41 BCE Legio XVII (Destroyed at the Battle of Teutoburg Forest 9 CE)
- c. 41 BCE Legio XVIII (Destroyed at the Battle of Teutoburg Forest 9 CE)
- c. 41 BCE Legio XIX (Destroyed at the Battle of Teutoburg Forest 9 CE)
- c. 31 BCE Legio XX Valeria Victrix
- c. 31 BCE Legio XXI Rapax
Caligula (37-41 CE)
- 39 CE Legio XXII Primigenia
Nero (54-68 CE)
- 66 CE Legio I Italica
- 68 CE Legio I Adiutrix or possibly levied by Galba
Galba (69 CE)
- 68-9 CE Legio VII Gemina Felix
Vespasian (69-79 CE)
- 70 CE Legio II Adiutrix
- 70 CE Legio IIII Flavia Felix to replace Legio IIII Macedonica
- 70-71 CE Legio XVI Flavia Firma to replace Legio XVI Gallica
Disbanded: for disloyalty during the Civil Wars of 69 CE.
- 70 CE Legio I Germanica
- 70 CE Legio IIII Macedonica
- 70 CE Legio XVI Gallica
Domitian (81-96 CE)
Destroyed: in the Dacian Wars (88-106 CE)
- 85-6 CE Legio V Alaudae
- 92 CE Legio XXI Rapax
Trajan (98-117 CE)
- 105 CE Legio II Traiana Fortis
- 105 CE Legio XXX Ulpia Victrix
Hadrian (117-138 AD)
Destroyed or Disbanded:
- c.120 CE Legio IX Hispana
- Possibly Lost or Disbanded during the uprising of 118 CE in Britannia
- c.135 CE Legio XXII Deiotariana
- Possibly Lost or Disbanded during Bar Kokhba's Revolt in Judaea.
Marcus Aurelius (161-180 CE)
- 165-6 CE Legio II Italica Pia
- 165-6 CE Legio III Italica
Septimius Severus (270-275 CE)
- 197 CE Legio I Parthica
- 197 CE Legio II Parthica
Severus Alexander (222-235 CE)
- 231 CE Legio IIII Italica
Valerian (253-260 CE)
- Lost or Disbanded: 260 CE Legio VI Ferrata
- Possibly during the Parthian Campaign where Valerian was taken prisoner and used as a footstool by the Persian King Shapur I.
Gallienus (253-268 CE)
- 260 CE Comitatenses Creation of an elite Cavalry Regiment.
Aurelian (270-275 CE)
- 274 CE Legio IIII Martia
Diocletian (284-305 CE)
- c.284-305 CE Legio I Jovia
- c.284-305 CE Legio II Herculea
- 296 CE Legio III Diocletiana
- 284-305 CE Legio V Jovia
- 284-305 CE Legio VI Herculia
Lost or Disbanded:
- c.290 CE Legio II Augusta Lost.
- c.312 CE Legio II Parthica Disbanded.
Julian (361-363 CE)
- 363 CE Legio I Armeniaca
- 363 CE Legio II Armeniaca
- Both Legions were created and used to invade the Parthian Empire.