This is a list of Roman legion

Roman legion

A Roman legion normally indicates the basic ancient Roman army unit recruited specifically from Roman citizens. The organization of legions varied greatly over time but they were typically composed of perhaps 5,000 soldiers, divided into maniples and later into "cohorts"...

s, including key facts about each legion,
primarily focusing on Principate

Principate

The Principate is the first period of the Roman Empire, extending from the beginning of the reign of Caesar Augustus to the Crisis of the Third Century, after which it was replaced with the Dominate. The Principate is characterized by a concerted effort on the part of the Emperors to preserve the...

 (early Empire, 27 BC - 284 AD) legions, for which there exists substantial literary, epigraphic and archaeological evidence.

Until the 1st century BC, Republican legions were temporary citizen levies, raised for specific campaigns and disbanded after them. By the early 1st century BC, legions were mixed volunteer/conscript units.