I was playing Total War: Rome II and Legionary Cohort unit in the game has mixed looking soldiers. You would have the classic looking Augustine soldier with the Lorica Segmentata and Scutum, Gladius etc. But then you would have a soldier with a Golden Helmet and Chainmail Armour, Republican Scutum. I was just wondering when was the classic Augustine soldier take up most or all of the cohort?
Roman legionaries were never uniformly equipped and in fact ring mail may have been more common than lorica segmentata. Although Trajan's column (built in the 2nd Century AD) depicts Roman legionaries universally wearing segmentata, the Tropaeum Traiani, interestingly does not show a single legionary wearing it. it was built at the same time, celebrates the same campaign, is situated on the frontier in modern day Romania and was probably made by soldier craftsmen. This questions the idea that lorica segmentata was worn by all legionaries by the second century.
It is unlikely that there was a definitive change over and adoption of lorica segmentata, especially as there were no centralised armouries in the first three centuries of the empire. There must have been large regional variation between different legions; perhaps the Praetorian guard were unviersally equipped with lorica segmentata, giving inspiration to the sculptors of Trajan Column but in the Danubian legions it was much rarer. By the third century AD lorica segmentata had been abandoned in favour of ring mail.
Lorica segmentata wearing legionaries never made up all of a legion and was only really worn in the first and second centuries.
I just want to correct you with this, but some of the legionaries in the cohort does not have golden helmets but bronze helmets. Imagine thousands of legionaries wearing golden helmets. It would be massively expensive and not effective at all.