User blog comment:SayuriDarling/The Mark of Athena Official Discussion/@comment-9592936-20130524184311/@comment-3146930-20130524191736

Or it could be the forces of Camp Half-Blood and Camp Jupiter marching on the Doors of Death, as they are technically foes. It could be both camps marching to the Doors of Death against the Gigantes. It could just mean the Seven of the prophecy and the remaining Gigantes.