Camelot's resident historian. Antonius was responsible for maintaining the archives of Camelot, including a key which would unlock the door to Merlin's library -- a forbidden place. Like many of Camelot's citizens, Antonius was not convinced that Merlin was not a dark wizard, and was therefore hesitant to associate himself with anything related to him.
At the behest of Dr. Daniel Jackson Antonius agreed to give SG-1 access to Merlin's library, but was unwilling to tempt fate after a secret passage to an underground room was revealed inside. He returned to his home, where a hologram of a Black Knight materialized and killed him.
Antonius had a wife, Livia.
Camelot - Antonius goes against his better judgment to admit SG-1 into Merlin's library, and pays for it with his life when the defense program activates in his bedroom.