In the early fourth century, the Roman Empire officially embraced Christianity. It now faced a new geopolitical adversary: the Sassanid Persian Empire, where Zoroastrianism was the state religion.

The Battle of al-Qadisiyah was fought in Mesopotamia — in present-day Iraq — in the A.D. 630s between Arab Muslims and the army of the Sassanid Persian dynasty during a period of Muslim expansion.

Originally constructed to house the Roman Emperor Valerian after his capture by Shapur I, the structure played a crucial role in the Sassanid Empire’s history. Following a decisive Persian victory ...