The Chronicles of Narnia
This book is set during the rule of the Pevensies. Shasta, is a young boy living in the country of Calormen. He decides to run away when he finds out he is not the son of Arsheesh.  He heads north to Narnia with a talking horse, Bree, a Calormene noblewoman, Aravis, and her talking horse, Hwin. It was published in 1954.