My understanding is the late empire had alot more cavalry and the Spartha and oval shield is better for cavalry. Why didnt the heavy infantry stick with the scutum and gladius?
How did Roman tactics change when the infantry switched to the Spartha and oval shield? Do the lines have more space between, etc.. ?
You will find answers here: https://www.reddit.com/r/AskHistorians/comments/28mt98/why_did_the_romans_changed_from_the_gladius_to/
It's Spatha, not Spartha, by the way.