Sagittarii

[1] Regular auxiliary units of foot and horse archers appeared in the Roman army during the early empire.

[3] In the early 1st century BC horse archers were already in widespread use and even supported Roman campaigns against the Germanic tribes in the Central Europe.

Possibly some of the other cavalry regiments there carried bows as back-up weapons, but were not the dedicated mounted archers that the sagittarii were.

The use of bows as primary weapons probably originated in the East in the later 4th and earlier 5th centuries to help the Roman army counter Persian and Hunnic bow-armed cavalry.

After the fall of the Western empire, Eastern Roman armies maintained their tradition of horse archery for centuries.