Use of 'old' equipment for later dates

[Nathan Ross]

Wouldn't it be possible/plausible for a simple legionary, who doesn't have that much to spend, to buy a second third fourth hand me down Coolus helmet?

There are Roman helmets with several different names punched into the rims (we discussed this here quite recently but I can't find the thread), so we know that this 'recycling' or passing on of older equipment must have gone on to some extent, and was probably quite common.

Excepting a few major changes in fashion or overall style (3rd to 4th century, for example), Roman military equipment tended to change relatively slowly, so there would be no practical reason why older types of equipment or armour would not have remained in use.

A lot of the time we can only date individual helmets or swords or whatever very approximately, and we have no way of knowing how long a particular style persisted. Mail and scale were used throughout the imperial period, alongside segmentata, and there are bronze 'Coolus' helmets dating the later 1st century. The 'Montefortino' style of helmet was apparently made and used for hundreds of years!