Magic Aegis - The Aegis Series, #1

The ancient witch Chloe's spell bound four men and their descendants to eternal duty protecting Kaereya from invasion. Generations later only the superstitious believe in witches and magic. Devastated by a false suitor, Vesper accepts the clansman Drew Montoren's offer of handfast. Confused and full of self-doubt, Vesper tires to accept her new life, but dream visions of approaching catastrophe torment her.