Jacob is the Eagle bearer, or Aquilifer, of the Twelfth Legion. It's supposed to be a great honor, but given that it involves carrying an empty pole — the Eagle having been lost in Alaska — Jacob is less than thrilled and quite embarrassed by his assignment.
He is seen holding the eagle when Octavian re-enlists Bryce Lawrence, watching with a look of concern on his face. He is also seen holding the eagle when Nico di Angelo, Will Solace, Lou Ellen Blackstone and Cecil Markowitz try to re-calibrate the aim of the onagers toward the other firing lines.
He participates in the archery lesson taught by Apollo and does alright. During the battle he is sprayed with Myrmekes acid and dies, a girl, Terrel, stayed by his side until the end and took over for him when he died.