The Battle of Alesia was one of the major game changers in ancient history, and led to the Roman conquest of Gaul.
Julius Caesar had been elected a Consul of Rome and was governor of Gaul for an unprecedented five years. He was also in command of his own personal army of four legions, and he wanted to conquer Gaul, which is in modern-day France, and the Gallic Wars occurred from 58-50 B.C. By 53 B.C. Caesar had subdued the Carnutes and the Eburones. However, there were many revolts against Roman rule, but Rome was very powerful then, and Caesar defeated them.
Vercingetorix was a leader of the Averni tribe, and called for a general rebellion against Roman rule and Julius Caesar. He gathered many tribes together and became the virtual king of Gaul. After a failed assault, Vercingetorix withdrew to Alesia, his capital. Caesar followed and laid siege on the city, and constructed fortifications around it. The only way out was right through Caesar’s army. It soon turned out that the Besiegers were themselves besieged by a Gaulish relief force. A joint attack by the relief force and Vercingetorix failed and was repulsed by the Romans. The next day Vercingetorix famously surrendered to Caesar and dropped his armor at his feet. He would be a prisoner of Rome for at least five years until his execution.
The Battle of Alesia was the end of organized resistance to Roman rule over Gaul, and also confirmed Caesar as the leader of Rome, which he became after a civil war.