The Abandonment of the Gladius for the Spatha - Why?

[Magnus]

Usually...you see a change in weapons in response to either a change in A) enemy armor/weapons or B) Enemy tactics. Usually. I don't put much stock in economic or logistic reaons behind outfitting the army with the spatha vs gladius. I'm fairly certain that even on the lowest level, an army will go to just about any length required to see that it gets the equipment it needs, especially while on active duty.

From what has been said, it really only seems as though the tactics have changed. From the close packed formations that utilized the tower shield, to a more open style where a longer bladed sword could be effectively wielded.

AND, it's interesting to note...that the sword likely wasn't the primary weapon on the battlefield. Even during the republic and early empire, was the pilum not considered the main weapon of the roman army? Sometimes battles didn't make it to where the sword was drawn, rather they were decided by javelin volleys. The same can be said of many other eras...the samurai for example. Primarily they were archers, spearmen, cavalry, shock troops and such. The katana was relied on as a side-arm. I don't see why the Roman army can be seen any differently.

My vote then is something changed in Roman tactics, or it was a response to the enemy's.