Brennus

Brennus led the Senones, a Gallic tribe, at a moment when Rome was still one power among many on the Italian peninsula. Around 387 BC, he defeated Roman forces at the Battle of the Allia, then pushed into the city itself with an army of Cisalpine Gauls. They occupied most of Rome and held it for several months—a humiliation the Romans would not suffer again for nearly 800 years, until the Visigoths broke through in 410 AD. The sack became a wound in Roman memory, proof that the republic had once been vulnerable, and a spur to the militarism that followed.