Sword moving from right to left

[Robert Vermaat]

The next painful question is, like the 'chicken or the egg', which change came first? The spatha or the oval shield? Date-line late 2ndC...
I tend to think that the need was for a longer weapon to reach more mounted foes, just as the hasta was being introduced into frontline service. The cylindical scutum may have proved difficult to use in combination with this longer weapon, used also for slashing as stabbing. An oval shield began to be introduced, and soldiers found they could shift the sword to the left, it made drawing the longer weapon slightly easier. The new shield also made slashing attacks over the top of the oval shield easier than over the top of the rectangular scutum.

Actually, both were around before that time. The auxilia used both the oval shield (no idea if these were flat or dished back then) as well as the spatha, plus they used a (shorter) hasta. However, I don't think they carried their swords on the left side, did they?

EDIT
I think the ayuxilia was used in a more versatile role on the battlefield (during the Principate) than the legioaries, who were basically mainly heavy infantry. Interestingly we see that same versatile role extended to the rest of Late Roman infantry, aswell as oval shields, hasta and spatha. Which makes it even more interesting to see whether earlier auxilia also wore swords on the left side or not.