Battle of Alesia - Siege and Battle

Siege and Battle

Alesia was a hill-top fort surrounded by river valleys, with strong defensive features. As a frontal assault would have been hopeless, Caesar decided upon a siege, hoping to force surrender by starvation. Considering that about 80,000 men were garrisoned in Alesia, together with the local civilian population, this would not have taken long. To guarantee a perfect blockade, Caesar ordered the construction of an encircling set of fortifications, called a circumvallation, around Alesia. The details of this engineering work are known from Caesar's Commentaries. About 18 kilometres of 4 metre high fortifications were constructed in about three weeks. This line was followed inwards by two four-and-a-half metre wide ditches, also four-and-a-half metres deep. The one nearest to the fortification was filled with water from the surrounding rivers.These fortifications were supplemented with mantraps and deep holes in front of the ditches, and regularly spaced watch towers equipped with Roman artillery.

Vercingetorix's cavalry often raided the construction works attempting to prevent full enclosure. The Roman auxiliary cavalry proved its value and kept the raiders at bay. After about two weeks of work, a detachment of Gallic cavalry managed to escape through an unfinished section. Anticipating that a relief force would now be sent, Caesar ordered the construction of a second line of fortifications, the contravallation, facing outward and encircling his army between it and the first set of walls. The second line was identical to the first in design and extended for 21 kilometres, including four cavalry camps. This set of fortifications would protect the Roman army when the relief Gallic forces arrived: they were now besiegers and preparing to be besieged.

At this time, the living conditions in Alesia were worsening. With 80,000 soldiers and the local population, too many people were crowded inside the plateau competing for too little food. The Mandubii decided to expel the women and children from the citadel, hoping to save food for the fighters and hoping that Caesar would open a breach to let them go. This would also be an opportunity for breaching the Roman lines. But Caesar issued orders that nothing should be done for these civilians and the women and children were left to starve in the no man's land between the city walls and the circumvallation. The cruel fate of their kin added to the general loss of morale inside the walls. Vercingetorix was fighting to keep spirits high, but faced the threat of surrender by some of his men. However, the relief force arrived in this desperate hour, strengthening the resolve of the besieged to resist and fight another day.

At the end of September the Gauls, commanded by Commius, attempted to break in by attacking Caesar's contravallation wall. Vercingetorix ordered a simultaneous attack from the inside. None of the attempts were successful and by sunset the fighting had ended. On the next day, the Gallic attack was under the cover of night. This time they met with greater success and Caesar was forced to abandon some sections of his fortification lines. Only the swift response of the cavalry commanded by Antony and Gaius Trebonius saved the situation. The inner wall was also attacked, but the presence of trenches, which Vercingetorix's men had to fill, delayed them enough to prevent surprise. By this time, the condition of the Roman army was also weak. Themselves besieged, food had started to be rationed and the men were near physical exhaustion.

On the next day, October 2, Vercassivellaunus, a cousin of Vercingetorix, launched a massive attack with 60,000 men, focusing on a weakness in the Roman fortifications (the circle in the figure) which Caesar had tried to hide, but had been discovered by the Gauls. The area in question was a zone with natural obstructions where a continuous wall could not be constructed. The attack was made in combination with Vercingetorix's forces who pressed from every angle of the inner fortification. Caesar trusted the discipline and courage of his men and sent out orders to simply hold the lines. He personally rode throughout the perimeter cheering his legionaries. Labienus' cavalry was sent to support the defense of the area where the fortification breach was located. With pressure increasing, Caesar was forced to counter-attack the inner offensive and managed to push back Vercingetorix's men. By this time the section held by Labienus was on the verge of collapse. Caesar decided on a desperate measure and took 13 cavalry cohorts (about 6,000 men) to attack the relief army of 60,000 from the rear. This action surprised both attackers and defenders. Seeing their leader undergoing such risk, Labienus' men redoubled their efforts and the Gauls soon panicked and tried to retreat. As in other examples of ancient warfare, the disarrayed retreating army was easy prey for the disciplined Roman pursuit. The retreating Gauls were slaughtered, and Caesar in his Commentaries remarks that only the pure exhaustion of his men saved the Gauls from complete annihilation.

In Alesia, Vercingetorix witnessed the defeat of his relief force. Facing both starvation and low morale, he was forced to surrender without a final fight. On the next day, the Gallic leader presented his arms to Julius Caesar, putting an end to the siege of Alesia.