Battle of Alesia

The Battle of Alesia (52 BCE) was the last decisive battle to be fought during the Gallic Wars between Julius Caesar and Vercingetorix.
It is famous for Caesar’s Military Tactic where he used Circumvallation and Contravallation to ward off and defeat a much bigger army.

September 52 BCE at Alesia, capital of the Mandubi Gallic Tribe.
Alise-Sainte-Reine is considered the most probable site of the Battle and is where the MuseoParc Alesia is now based.

Having avoided a protracted siege at the Battle of Gergovia, Caesar moved his six Legions north to join Labienus.
Labienus, like Caesar, had been unable to engage the Senones and Parisi in a Battle where he could exploit the superior Roman Military Tactics.
Finally, near Lutecia, Labienus broke the Gallic Cavalry and killed the Commander, Camulogenus, and routed the Gallic armies. This removed any threat from northern Gaul. Labienus took supplies from Agendicum and marched to unite with Caesar’s Legions.
The ten Legions then marched to meet the army of Vercingetorix.

Rome

Gaul

Estimated: 180,000 – 330,000 men (Plutarch states 300,000)
Besieged: 80,000
Allied Cavalry: Aedui 15,000
Casualties and Losses:
- Relief Army: 56,000-90,000
- Besieged Army: 40,000 captured.

Julius Caesar's Strategy
- Caesar now had 10 Legions under his Command. He left 20 Cohorts to defend the Gallic Tribes who were still in Alliance with Rome.
- However, he had lost the Aedui, whose 15,000 cavalry now went over to Vercingetorix. So instead, Caesar called on the German Tribes to send their Cavalry.

Vercingetorix‘ Strategy
- At a Council of the Gallic Tribes, Vercingetorix was elected Commander of all the Gallic Armies. This made him, de facto, King of the Gauls.
- He decided to attack Caesar’s Army which had just reunited and was on the move, encumbered by its Baggage Train.

Vercingetorix attacks Caesar’s Army on the Move
- Near Divio (Dijon), Vercingetorix attacked the front and rear of Caesar’s column with his Cavalry. However, Caesar sent the German Cavalry to counter-attack and dispersed the Gallic Cavalry, leaving the Gallic Infantry exposed.
Vercingetorix is forced to retreat to Alesia.
- Vercingetorix was now obliged to retreat with his army and made his way to the well fortified mountain top city of Alesia, where he prepared for a long siege and to wait for the Relief force under Commius.

Caesar decided on a prolonged Siege to starve the 80,000 soldiers and the resident population into submission.

In three weeks he built a ‘Circumvallation consisting of lines of embankments and entrenchments and towers at intervals, facing the besieged, with an 11 mile (18km) wall 13 ft (4m) high, encircling the city, to prevent entry or escape.
The trenches were 14 ft (4.5m) deep and filled with mantraps, such as the Caltrop.

After a group of Vercingetorix‘ cavalry escaped to get help, Caesar built a second line of fortifications.
This was a 13 mile (21km) long barrier, facing away from the city, with four cavalry camps. It was designed to protect the besiegers from an allied army attempting to break through and rescue the defenders in the city.

As their were insufficient supplies for everybody in the city, Vercingetorix released the civilians, hoping Caesar would let them through.
Instead, to keep pressure up on the besieged and force them to surrender, he gave orders that no one was to be let through. They then proceeded to starve outside the walls, in the front of their kinsmen.

When the Relief Force arrived and started its attack, Vercingetorix attacked simultaneously from inside the city.
The next day the Gauls decided to attack the outer lines by night, and Caesar started losing certain areas until his cavalry under Mark Anthony and Gaius Trebonius, retrieved the situation.
Vercingetorix attacked the inner lines but lost the element of surprise due to the time taken to fill the ditch before they could cross it.
The Romans were becoming tired and also morale and supplies were getting low.

On the 2nd October, a weak area where the defensive wall were not continuous, was found in the outer lines and 60,000 Gauls attacked it. At the same time Vercingetorix attacked the same area from the inside.
Caesar ordered Labienus to simply hold the lines, but his forces were starting to give under the combined attack.
Caesar first counterattacked Vercingetorix who was successfully pushed back.
Caesar then took 13 Cavalry Cohorts (c. 6,000 horse) outside the Contravallation, and attacked the 60,000 Gauls in the rear.
The result was panic and the relieving army collapsed and retreated. They were almost annihilated by the disciplined Romans.

On the 3rd October, realising that the relief force was now defeated, and with no supplies to withstand the Siege, Vercingetorix was forced to surrender the city without giving Battle. He rode out and personally surrendered his arms to Julius Caesar.
He hoped for clemency based on the fact that he and Caesar had once been friends, but Caesar was unmoved.
Vercingetorix was subsequently imprisoned in the Mamertine Prison in Rome for five years, before being executed.

The Aedui and the Arverni were pardoned and again became important Roman Allied Tribes.
The rest of the Gallic Defenders and the remnants of the Relief army were sold into slavery.

Having defeated the last Alliance of Gallic armies, the Battle resulted in the conquest of Gaul. It was the last time an Alliance of the Gallic Tribes attempted to defeat Rome. Gaul now became a Roman Province for the next 400 years.
The Battle is noted as being a classic example of Siege Warfare and Roman Engineering achievement in the art of Circumvallation and Contravallation.
The Roman Senate awarded Julius Caesar a Supplicatio of 15 days.
However, opposition was growing in the Roman Senate to Caesar, and he was not permitted to have a Roman Triumph to celebrate this great victory.
This led to the Great Roman Civil War.

MuseoParc Alesia