Prior to the Muslim conquest of Persia, the primary religion in the area was Zoroastrianism.

Constantine the Great became the first Christian Emperor being baptized in 337AD. After leading a series of successful military campaigns to reclaim Roman frontier land lost in the previous century, Constantine rose to the rank of emperor. After a series of gold coin reforms to curb inflation, he allowed the Edict of Milan in 313, which claimed tolerance of Christianity throughout the empire. He oversaw First Council of Nicaea in 325 and moved the capital to Constantinople in Byzantium. He was baptized on his deathbed, as was tradition in the day for practicing Christians.

The strong resemblance between the Greco-Roman pantheon of Gods and the Vedic pantheon demonstrates how widespread religious sharing could be during the ancient and classical eras. Many religious stories and traditions were shared over thousands of miles and became part of the foundational myths of extremely diverse societies.

Household shrines to ancestors were an important component of Roman worship. Romans, particularly during the period of time known as the Roman Republic, practiced ancestor veneration. They built household shrines to ancestral spirits, so that those spirits could be soothed and revered and so that they would not turn malevolent.

Mahayana is the one of the two major denominations of Buddhism - along with Theravada. Mahayana emerged in China, Korea, and Japan as a result of religious syncretism following the spread of Buddhist teachings into this part of the world.

Confucianism and Daoism both originated in China, and would therefore most likely be found there. Hinduism and Buddhism would be more likely to be found in India. Zoroastrianism, Judaism, or Christianity would more likely be found in Persia. Lastly, Greek rationalism or potentially Christianity would be more likely found in Greece.

Constantine was the emperor that drafted the Edict and moved the capitol to Byzantium, and he was the first Roman emperor to have any sort of tolerant position for Christians. Julius and Augustus lived before the birth of Christ, and both Nero and Caligula lived centuries before the Edict was passed, so none of the others could have possibly drafted the Edict.

In the Hindu faith Brahma is known as the Creator or the World Soul. Brahma is one of the most popular deities in the polytheistic Hindu faith.

Theravada and Mahayana are the two major denominations of Buddhism. Theravada developed in India and southeast Asia and is simpler and more closely related to the original teachings of Buddha than Mahayana. Mahayana is primarily practiced in East Asia and involves more ritual practices and ceremonies that are unrelated to the teachings of Buddha. This difference occurred because as Buddhism spread to countries like China, Korea, and Japan it absorbed some elements of local religious customs.

One of the reasons that Christianity spread around the Roman Empire was because it was so popular among those who were powerless or disenfranchised in Roman society (which was the vast majority of the population). Christianity was rapidly embraced by non-citizens, slaves, the rural poor, the urban poor, and women.