The extraordinarii were the elite troops of the Roman alae, recruited from the socii, Rome's Italian military allies.
The standard Consular army of the Republic was made up of two legions and a comparable number of Italian allied troops, termed the alae.
Franz Fröhlich, in his work on the Guard troops of the Roman Republic,[10] speculates that they were created shortly after the Latin War, which ended in 338 BC.
Polybius, writing after 146 BC, describes the extraordinarii in detail as referenced above, though there are few mentions of these troops in other sources at this time.
The formation was presumably phased out with the so-called Marian reforms when the separation between citizen legions and alae was abolished.