I have been slowly updating, and I hope improving, the page here on this website with the brief summaries of the stories that Rosemary Sutcliff tells in her books. So, A Circlet of Oak Leaves (from 1968):
Gradually reveals the mystery behind a humble horse-breeder Aracos’s award for outstanding bravery. It tells the story of a daring exploit when Roman auxiliaries and legionnaires fought the Picts on the northern borders of England. Standing in for Felix, a legionary sick with fear before a battle, he fights with great courage and then sees Felix receive the Corona Civica for what he has been through.