Caius

 was a legionary who arrested the Fifth Doctor during a riot in Nicaea in 325. He told Emperor Constantine I about the riot and brought the Doctor to him. The next day, he was annoyed that Erimem was at the Council of Nicaea. He later caught Peri Brown and Erimem and took them to the Emperor. He often guarded the Emperor. (AUDIO: The Council of Nicaea)