To Pass Through Shadow and Fire
Mathilda sat where she always sat, among the oldest students, young women who would be passing through the shadow and the fire come the dark of the year. A few would emerge as Ladies [of the Wood] of full power and learning. Many would die in the testing.
— Judith Tarr, Rite of Conquest, Chapter 17
Every year at Beltane, one or more of the young women in the acolytes’ house passed through darkness and fire. Then they were Ladies of the Isle; or they were gone.
— Judith Tarr, King’s Blood, Chapter 33
Emphases mine.