He saw Percy at the end of the Via Principalis, holding off the army of ghosts. He’d overturned the chariot and destroyed several buildings, but every time he threw off a wave of attackers in his hurricane, the ghosts simply got up and charged again. Every time Percy slashed one of them down with his sword, the ghost re-formed immediately. Percy had backed up almost as far as he could go. Behind him was the side gate of the camp, and about twenty feet beyond that, the edge of the glacier.

The Son of Neptune, Chapter XLVI