Under the employment of a Roman lanista, Polymestor fought in many battles in the Cyrene Gladiator Arena, including one against Julius Caesar, who spared the gladiator and gave him a sword. Having grown tired of the fortune he gained over his victories, Polymestor escaped from the lanista's services along with the prized sword. As a result, the lanista pursued the former gladiator throughout Kyrenaika in an attempt to recover the sword.
At some point in 47 BCE, Polymestor was given refuge by a group of silphium farmers. Believing that staying in the farm would bring the farmers misfortune, Polymestor left the farm to start a new life at a nearby fishing village, throwing the sword away in the waters nearby. The lanista learned of his stay at the farm and sent his men to eliminate the farmers that had aided him.
Polymestor's whereabouts were eventually discovered by the Medjay Bayek, who was hired by the lanista to locate him and recover the sword. Polymestor directed Bayek to sword's location, allowing him to recover the sword. Moments later, the lanista and his men arrived to confront Polymestor, seeking to reclaim the sword. However, the lanista's attempt was stopped by Bayek, who recovered the sword and helped Polymestor to eliminate the Romans.
With the lanista dead, Polymestor allowed Bayek to keep the sword. He could then finally retire from his life as a gladiator and become a fisherman as well as start a family.