The Boar Stone by Jules Watson

(Published in the U.K. as The Boar Stone)

Roman Britain, 366 AD: Minna, an eighteen-year-old Roman serving girl, leads a quiet life with her grandmother, a Celtic herbal healer. But when her beloved grandmother dies, Minna must make a difficult choice--marry a man she loathes, or venture out alone to track down her brother, a soldier in a Roman garrison stationed in the wartorn and wild Scottish borderlands.

Desperate to find her brother, Minna falls in with Cian, an aloof but charming young acrobat. A terrible mistake thrusts the pair into slavery in the wilds of barbarian Scotland, where the Romans wage war on the violent, blue-tattooed Picts in Eastern Scotland. Cahir, King of the Dalriadans of western Scotland, is caught in the middle of a war that will seal the fate of the Scots. Year by year, Cahir has watched in shame as his people fall under the Roman yoke. Now Cian and Minna, unwilling prisoners at Cahir's fort, must fight for their survival. And despite her loyalties to her Roman blood, as the war for Scottish freedom unfolds, Minna struggles against another force--an irresistible call of her blood that reveals a destiny she shares with the wounded king Cahir, and which binds her inevitably to the people who have enslaved her.

This book is part of the "Dalriada Trilogy" series.
Here are some other books from this series: