Darkwitch rising / Sara Douglass.

Enhanced descriptions from Syndetics:

DARKWITCH RISING is the third title in Sara Douglass's compelling Troy Game series, a riveting historical fantasy series of love and revenge set against the very fabric of time itself.
Britian. An ancient land. Most think they know its history. But few suspect and fewer still know the truth.
For back in the mists of time came Brutus, last of the Trojan kings, who was armed with the knowledge of how to construct a magical Labyrinth that could rival the might of the gods. He was drawn to this place by the alluring sorceress Genvissa and together they almost succeeded in creating the Labyrinth. But in the end they were thwarted by Brutus's wife Cornelia, who understood the danger to the land. Her actions however trapped them all into a endless cycle of death and rebirth until the magic of the Labyrinth is completed.
Ages pass. Time and again the players have come close to victory but each time there is a new wrinkle to stay the fulfillment of power.
The Now that these soul travelers arrive is a most unique one. The English are at war, not with a foreign power but amongst themselves; a mighty Civil War that threatens to destroy a nation. A great pestilence is upon the land and the newly restored Charles II sits upon the throne trying to hold chaos at bay...and he is one of the major players in this drama.
And he is not alone.