In late Antiquity, religion played a central role in identity formation between the 4th and 7th centuries. Religious policies were decisive in the relations between the Roman and Sassanid Empires. The acceptance of Christianity in Rome during the reign of Constantine the Great increased suspicions of Christians in the Sassanid Empire. Šāpur II (309-379) questioned the loyalty of his Christian subjects and imposed heavy taxes on them, asking the bishop Siemon bar Sabba’e to collect these taxes. Shimon was martyred for his refusal. During this period, the Sassanid rulers oppressed not only Christians but also Armenians and Jews in terms of their religious loyalty. There were converts among the Armenian nobility, some of whom were loyal to the Sassanid administration. Šāpur II’s religious policies were not only an economic tool but also a political one. Taxes and religious oppression were used to reduce the Christian population and make them submit to Sassanid authority. Although contemporary studies argue that these policies were motivated by financial concerns, sources clearly reveal Šāpur II’s aim to control the religious population. This study examines Christians’ social and political status in 4th century Iran through the martyrdom of Siemon bar Sabba’e, imperial policies, and taxes.