"The same brave Cassius Chaerea"

Cassius Chaerea is mentioned by Tacitus and Suetonius, so he is not an "invented" character, but his persona in the novel is largely invented by Graves. Tacitus tells us that he distinguished himself in the German campaign, but Graves invents the story about him being a survivor of the Teutoberg Forest massacre, along with his role in the mutiny at Bonn, his early encounter with Caligula and his feat of bravery in the amphitheatre. Like Calpurnia, he becomes a significant character later in the story.