User blog comment:SayuriDarling/Full first chapter of The Mark of Athena/@comment-4606607-20120613003935/@comment-5175468-20120701005726

It is probably a dream. Or maybe a forced War Games between the two by Octavian (sorry, sometimes crazy ideas that are possible pop into my head).

Most likely it is Annabeth's dream. If not, the fourth narrator who is probably worried about what would happen if the Greeks and Romans did not get along and they end up breaking into a full out war.