First Legion
- 1st Brigade, Polish Legions
- 1st Legion Tercio "Great Captain Gonzalo Fernández de Córdoba"
- 1st Legions Infantry Division (Poland)
- Legio I Adiutrix
- Legio I Armeniaca
- Legio I Germanica
- Legio I Iovia
- Legio I Isaura Sagittaria
- Legio I Italica
- Legio I Macriana liberatrix
- Legio I Maximiana
- Legio I Minervia
- Legio I Parthica
- List of Roman legions
- The First Legion