Lucius Aelius Rufus was a Roman officer and magistrate whom the Tenth Doctor met at a way house during his two day journey to Rome. Lucius was on business for the emperor, and had been travelling to Rome from Gaul. Gnaeus had heard of him, and winced upon hearing him enter the building.
Lucius had reserved a fresh horse, which was mentioned between him and the inn keeper. Over-hearing this, the Doctor reminded the keeper that he had said that there were no more fresh horses. Caught in his lie, the keeper admitted to having just the one, but it was unavailable. After this, the Doctor casually left the building. The sound of hoof beats soon followed, and Lucius, Gnaeus, and Lucius' guards ran outside to see that the Doctor was riding off with the stolen horse.
Two days later, Lucius had managed to make it to Rome and pinpoint the Doctor's location. He had him arrested in the temple of Fortuna and taken to the Colosseum prisons. While there were no games that day, there would be fights the next, and the Doctor was to participate in them.
After being thrown into the arena, the Doctor saw that Lucius was there to watch him be killed by the trained animals. After a fierce fight, the attempt by all the prisoners to escape succeeded, and Lucius was killed when he attempted to cut the rope that the prisoners were using to escape. He fell over the fence dead when George threw a trident and it nailed him in the chest. His body fell into the arena, distracting a panther and allowing the last of the prisoners to escape. (PROSE: The Stone Rose)