The Dalemark Quartet Series Novels

The Crown of Dalemark (The Dalemark Quartet 4) by Diana Wynne Jones
The Spellcoats (The Dalemark Quartet 3) by Diana Wynne Jones
Drowned Ammet (The Dalemark Quartet 2) by Diana Wynne Jones
Cart and Cwidder (The Dalemark Quartet 1) by Diana Wynne Jones