Circle of Days by Ken Follett

A FLINT MINER WITH A GIFT
Seft, a talented flint miner, walks the Great Plain in the high summer heat, to witness the rituals that signal the start of a new year. He is there to trade his stone at the Midsummer Fair, and to find Neen, the girl he loves. Her family lives in prosperity and offer Seft an escape from his brutish father and brothers within their herder community.
A PRIESTESS WHO BELIEVES THE IMPOSSIBLE
Joia, Neen’s sister, is a priestess with a vision and an unmatched ability to lead. As a child, she watches the Midsummer ceremony, enthralled, and dreams of a miraculous new monument, raised from the biggest stones in the world. But trouble is brewing among the hills and woodlands of the Great Plain.