Why change to the Spatha?

[Robert Vermaat]

And don’t forget that that during the imperial age, the enemy had improved its armor after repeated decades of loses

Had they? Didn't the enemies of the 3rd and 4th centuries include mainly Germanic and Gothic people with little or no armor?

Hi Matthew,

No, that´s not correct. If at all, the armour of the Germanic foes would have increased during this period.

I´m still of the opinion that the style of fighting amongst the enemy made the difference. In the East, I guess there was not that much difference between Parthian and sassanian armoured cavalry, but even so as an infantryman I would like a longer sword more than a short one, I mean, after I´ve lost my trusted spears.
But in the West, the enemy had changed - from onrushing droves, the German foes had learned to team up and fight in formations that could no longer be broken up easily. Apparently, the gladius as a side-stabber would no longer do when a shield wall was just that - a wall of tall shields. So you needed a bit of reach to get unarmoured bits of the enemy, something offered by the spatha rather than the gladius, maybe?