Every year on Christmas, Christians celebrate the birth of their religion's founder, Jesus from Nazareth of Galilee. Part of this celebration includes the claim that Jesus was born from a virgin mother named Mary, which is fundamental to the Christian understanding that Jesus is the divine son of God.

The virgin birth may seem strange to a modern audience – and not just because it runs counter to the science of reproduction. Even in the Bible itself, the idea is rarely mentioned.

As a scholar of the New Testament, however, I argue that this story's original audiences would not have been put off by the supposed "strangeness" of the virgin birth story. The story would have felt much more familiar to listeners at that time, when the ancient Mediterranean was full of tales of legendary men born of gods – and when early Christians were paying close attention to the Hebrew Bible's prophecies.

What the Bible does – and doesn't – say

Strikingly, the New Testament is relatively silent on the virgin birth except in two places. It appears only in the gospels of Matthew and Luke, written a few decades after Jesus' death.

The Book of Matthew explains that when Joseph was engaged to Mary, she was "found to be pregnant through the Holy Spirit." The writer links this unexpected pregnancy to an Old Testament prophecy in Isaiah 7:14, which states "the virgin will conceive and give birth to a son, and she will call him Immanuel." According to the prophet Isaiah, this child would be a sign to the Jewish people that God would protect them from powerful empires.

Now the majority of early Christians outside of Judea and throughout the Roman empire did not know the Old Testament in the original Hebrew, but rather a Greek translation known as the Septuagint. When the Gospel of Matthew quotes Isaiah 7:14, it uses the Septuagint, which includes the term "parthenos," commonly understood as "virgin." This term differs from the Hebrew Old Testament, which uses the word "almah," properly translated as "young woman." The slight difference in translation between the Hebrew and the Greek may not mean much, but for early Christians who knew Greek, it provided prophetic proof for Jesus' birth from the Virgin Mary.

Was the belief in the virgin birth based on a mistranslation? Not necessarily. Such terms were sometimes synonymous in Greek and Jewish thought. And the same Greek word, "parthenos," is also found in Luke's version of the story. Luke does not cite the prophecy in Isaiah 7:14. Instead, this version of the Nativity story describes the angel Gabriel announcing to Mary that she will give birth even though she is a virgin. Like in Matthew's version of the story, Mary is told that her baby will be the "son of God."

Human and divine?

For early Christians, the idea of the virgin birth put to rest any rumors about Mary's honor. It also contributed to their belief that Jesus was the Son of God and Mary the Mother of God. These ideas became even more important during the second century, when some Christians were debating Jesus' origins: Was he simply born a human being but became the Son of God after being baptized? Was he a semi-divine being, not really human? Or was he both fully divine and fully human?

The last idea, symbolized by the virgin birth, was most accepted – and is now standard Christian belief. But the relative silence about it in the first few decades of Christianity does not necessarily suggest that early Christians did not believe it. Instead, as biblical scholar Raymond Brown also noted, the virgin birth was likely not a major concern for first-century Christians. They affirmed that Jesus was the divine Son of God who became a human being, without trying to explain exactly how this happened.

Greco-Roman roots

Claiming that someone was divinely born was not a new concept during the first century, when Jesus was born. Many Greco-Roman heroes had divine birth stories. Take three famous figures: Perseus, Ion and Alexander the Great.

One of the oldest Greek legends affirms that Perseus, an ancient ancestor of the Greek people, was born of a virgin mother named Danaë. The story begins with Danaë imprisoned by her father, the king of Argos, who feared her because it was prophesied that his grandson would kill him. According to the legend, the Greek god Zeus transformed himself into golden rain and impregnated her.

When Danaë gave birth to Perseus, they escaped and eventually landed on an island where he grew up. He eventually became a famous hero who killed the snake-haired Medusa, and his great-grandson was Hercules, known for his strength and uncontrollable anger.

The playwright Euripides, who lived in the fifth century B.C., describes the story of Ion, whose father was the Greek god Apollo. Apollo raped Creusa, Ion's mother, who abandoned him at birth. Ion grew up unaware of his divine father, but eventually reconciled with his Athenian mother and became known as the founder of various Greek cities in modern-day Turkey.

Lastly, legends held that Zeus was the father of Alexander the Great, the Macedonian ruler who conquered his vast empire before age 33. Alexander was supposedly conceived the night before his mother consummated her marriage with the king of Macedon, when Zeus impregnated her with a lightning bolt from heaven. Philip, the king of Macedon, raised Alexander as his son, but suspected that there was something different about his conception.

A familiar type of hero

Overall, divine conception stories were familiar in the ancient Mediterranean world. By the second century A.D., Justin Martyr, a Christian theologian who defended Christianity, recognized this point: that virgin birth would not have been considered as "extraordinary" in societies familiar with Greco-Roman deities. In fact, in an address to the Roman emperor Antoninus Pius and philosophers, Justin argued that they should tolerate Christian belief in the virgin birth just as they did belief in the stories of Perseus.

The idea of the divine participating in the conception of a child destined for greatness wouldn't have seemed so unusual to an ancient audience. Even more, early Christians' interpretation of the prophecy in Isaiah 7:14 from the Septuagint supported their belief that Jesus' origin was not only divine, but foretold in their prophetic scriptures.

Rodolfo Galvan Estrada III is Assistant Professor of the New Testament at Vanguard University. This article is republished from The Conversation under a Creative Commons license.