Forget the Romans!
Look at our own stuff: F-16 fighter/bomber, 40 years old. AK-model rifles, nearly 70 years old for the original, 40 for the current Russian standard rifle. Steyr AUG rifle, 1978. SA-80, 1985. M-2 .50 cal machine gun dates from WW 2. Panavia Tornado, 1974. Even the Eurofighter is 20 years old.
Improvements for troops include better body armour, but you can't easily see that.
In any case, technology runs up against physics. That's why we got to the best possible rocket motors in the 60's and haven't done better since.