You know what I mean: Legionaries wear red cloaks and Praetorians wear blue, they wear the Lorica Segmentata, they carry big rectangular shields with eagle wings and lightning bolts on them, the cavalry have oval shields, and standard-bearers wear wolf skins. But why to we have this image that this was what the Roman Army looked like, and, dare I ask, is it accurate?
The two-word answer: Trajan's column.
For past answers to this question the long and detailed reply by u/TheLoudOne1 and my much shorter one in https://www.reddit.com/r/AskHistorians/comments/apzyyv/picture_a_roman_soldier_odds_are_that_youre/