The story of Mani, the founder of Manichaeism.
An interesting picture of 3rd century Mesopotamia (now Iraq/Iran) as Mani tries to unite all of the religions of his time in a simple pacifistic belief system with support from the Emperor Shapur of the Sassanid dynasty but open hostility from the entrenched priesthood.
#BookedInTime
Shapur's war with Rome does get a couple of chapters