On a hot and dusty plain eight miles from the Roman city of Adrianople, on August 9, 378 A.D., the elite field army of the Eastern Roman Empire and a tribal army of refugee Visigoths fought one of the most celebrated battles in western military history. The results would reverberate for centuries.
The late Roman legion used round shields because the Roman state didn't have the money to train the soldiers to work as an organized fighting machine like the early legion was. Instead the late legion was a militia and hence had to use round shields because round shields are better in individual combat.
Battle of Adrianople. On August 9, 378 c.e., the Eastern Roman army under the command of Emperor Valens attacked a Gothic army (made up of Visigoths and Ostrogoths) that had camped near the town of Adrianople