Warmatrix

The Battle of Alesia in 52 BCE is a showcase of the discipline and engineering skill of the Roman army.
The Romans under Gaius Julius Caesar had been busy conquering Gaul from 58 BCE, but the Gauls were far from subdued. They rebelled several times. In the winter of 54 - 53 BCE a Gallic army under Ambiorix ambushed the 14th legion and destroyed it. It took Caeasar the entire year to put the rebellion down. The next winter all but two tribes, deciding to kick the Romans out once and for all time, formed an alliance and elected Vercingetorix as their leader. When Caesar became aware of the renewed revolt, he crossed the Alps in winter snow and raced towards his army, rallying it just in time. Vercingetorix employed a terrible scorched earth tactic that hurt Romans and Gauls alike. Caesar engaged the Gauls at the hill fort of Gergovia but was forced to retreat. Later he scored several victories and Vercingetorix retreated to Alesia, another hill fort, probably hoping to force the Romans to an attack equally costly as that at Gergovia.
Alesia was a strong position due to its location on a hill between two rivers, and also its walls. Caesar saw that a frontal assault with his troops (estimated at only 50,000 - 60,000) would be useless and instead settled on a siege. As there were 80,000 infantry plus 15,000 cavalry in the fort plus civilians, starving them out should haven taken little time. To prevent the Gauls from breaking out and fetching supplies, he let his army construct a circumvallation around Alesia. It was a 18 kilometers long wall supplemented by two ditches 2.5 meters deep and 4.5 meters wide, mantraps and watchtowers.
The Gauls repeatedly tried to break out, were beaten back several times by the Roman and allied Germanic cavalry, but after some weeks a detachment managed to break through. They were off to call in Gallic reinforcements. Instead of abandoning the siege, Caesar ordered further constructions to keep the relief force out. A second line, a contravellation, was set up, nearly identical to the first. The Gauls inside Alesia, by now very hungry, expelled the civilians, hoping that Caesar would let them go. But he did not, so they were forced to dwell in the no-mans land between the walls.
In September the Gallic relief force, by modern estimates around 80,000 - 100,000 strong, arrived. Several times they tried to break in while Vercingetorix simultaneously tried to break out. Under this pressure, the Romans had to abandon some of their fortifications, but could regain them before the Gauls had overcome the trenches. The Roman cavalry proved to be a vital asset in these operations and killed many Gallic light troops. In October the Gauls attacked again, possibly with 60,000 men, targeting a weak point in the defenses in the northwest. The Romans, by now also starving and exhausted, nearly broke down. Caesar, in a desperate attempt to stem the tide, with 6,000 cavalry personally led a counterattack on the Gallic relief force. This surprised the Gauls and rallied the morale of the Roman infantry. The Gauls where scattered and suffered heavy losses. The battle was won, though it had been a very close call.
Now cut off from the rest of the world without hope of rescue, Vercingetorix surrendered without a fight. Tens of thousands of Gauls were sold into slavery and the leader was paraded around in Rome, then executed. Alesia broke the resistance to Roman rule and made Caesar definitive master of Gaul. It greatly increased Caesar's prestige, eventually leading to a showdown with the Roman senate.