Which major battle marked the beginning of the decline of the Roman Empire?

The Battle of Adrianople

The Battle of Adrianople, which occurred in 378 AD, is often cited as the beginning of the decline of the Roman Empire. Emperor Valens was defeated and killed by the Goths in this battle, a defeat that not only cost a Roman emperor his life but also demonstrated Rome's vulnerability to the Germanic tribes. This military disaster marked a turning point, illustrating the internal weaknesses of the empire and accelerating the external pressures that would eventually lead to its fall. The Battle of Adrianople had a profound impact on the military and political structure of Rome, highlighting the challenges the empire faced in managing its vast borders.