The battle took place between the forces of the Roman Empire, which consisted of five Roman legions commanded by Gaius Antistius Vetus and the forces of the Cantabri people, who had fortified the hill fort at Aracillum.

The Roman commander, Gaius Antistius Vetus had taken charge of Caesar's legions when Augustus had fallen ill on the campaign (though Caesar did conduct a majority of the battles in this campaign himself).

The Romans constructed more than 20 kilometers of walls, battlements and trenches (circumvallatio) to trap the defenders inside the fort and to prevent any aid or reinforcements from gaining entrance.

In the face of starving to death, many of the Cantabri warriors opted instead to commit suicide rather than dying of starvation or being taken prisoner and being turned into slaves.

Traditionally identified as Aradillos [es] (Campoo de Enmedio), there has never been any concrete discovery of the actual location of the battle.