The Battle of San Francisco Bay is the battle that consisted of the second wave of Caligula's Assault on Camp Jupiter.
As they are on their last leg defending the Caldecott Tunnel, Commodus and Caligula arrive to demand the legion's surrender. However Frank Zhang declares spolia opima, single combat to the death. Unable to refuse in front of their soldiers, they accept and Apollo joins in with the former god fighting Commodus and the son of Mars fighting Caligula. During the fight, Frank lures Caligula to a hidden cache of Greek Fire and burns his stick, triggering a massive explosion which kills Caligula and badly maims Commodus. As the emperor’s forces are in shock, Commodus manages to order a bombardment on Camp Jupiter from the Julia Drusilla Yachts. Apollo then kills Commodus. However, thanks to the efforts of Lavinia Asimov and her group of nature spirits, the Greek Fire projectiles land back on the yachts and destroy them. The emperors forces flee in shock and fear, believing that Apollo was responsible.
Apollo heads to New Rome to help, along the way running into Meg McCaffrey and Hazel Levesque and head to Cyclops Books to defend Tyson and Ella from Tarquin. However, Tyson and Ella remained in the Temple of Diana, causing the small group to find only Tarquin and the undead king's forces. Tarquin then forces Apollo to reveal their local and he tries and fails to summon more zombies to pillage the city, but nothing happens. Meg fights Tarquin's zombies and destroys them while Hazel defeats the undead king. Diana finally arrives with the Hunters of Artemis who help to stop the second wave of zombies. Diana kills Tarquin with an arrow to the head, causing his remaining zombies to dissolve.
In the aftermath of the battle, the total number of both legionnaires and civilians of New Rome is so low that all survivors can fill up only one building.