Constantine the Roman emperor was angry, and bore it ill when he heard of the sufferings to which the Christians were exposed in Persia. He desired most anxiously to render them assistance, yet knew not in what way to effect this object. About this time some ambassadors from the Persian king arrived at his court, and after granting their requests and dismissing them, he thought it would be a favorable opportunity to address Sapor in behalf of the Christians in Persia, and wrote to him,
Christianity · Church History · Ecclesiastical History
Book II, Ch. 15 — Constantine writes to Sapor to stay the Persecution of the Christians.
Ecclesiastical History · Salminius Hermias Sozomen