During Aurelius Ambrosius time the weapons change quite a lot from earlier periods. Most of the invention lies in adapting the weapons to the more modern armor and shields that start showing up. The weapons are more well built, allowing them to be lighter and easier to maintain. Also, more weapons are produced because of all the wars.
After the Roman Empire leaves the empire much of the effective roman weapon-industry disappears and much of the earlier weaponry disappears. Some of the larger roman cities retain an ability to produce the weaponry but older tribal weaponry becomes more common.