Orion and the Conqueror by Ben Bova (Review).

Orion finds himself in the times of Phillip the King of Macedonia where he encounters many a battle as a seasoned time traveler in this engaging science fiction thriller. The creators again have control over the space-time continuum and use Orion as a tool to keep the continuum manageable by the creators. Orion finds himself empowered to the point he warns Phillip of Macedon of an assassination plot on his life. Alexandros the heir apparent or the King himself must die in order for the creators to leave the time period, and Orion is simply the tool the creators use to their own end. Still struggling to find his love Anya, who is lost light-years from Orion's situation, seems to be the long drawn out ambition of Bova, as I'm sure the series will continue. This is just a stop in time where history is latered to the author's satisfaction, but in the author's note, most everything about King Phillip and Alexandros is historically accurate. I'm not sure what part of his series or volume I've fallen into, but this is a very worthy read. The whole notion of time-travel makes science fiction opening a whole new world of scientific theory, treading on the unbelievable and yet escaping with the possibilities of space/time travel.