Some intriguing history here, via the BBC:
Christianity, Buddhism, Hinduism, Zoroastrianism and Greek mythology are usually regarded as utterly distinct religions, largely defined by their differences. But if you just look at them, you will see a symbol that connects them all – the halo.
Why was this symbol invented? It has been conjectured that it could have originally been a type of crown motif. Alternatively, it may have been a symbol of a divine aura emanating from the mind of a deity. Perhaps it was a simple decorative embellishment. One amusing proposal was that it derived from protective plates fixed to statues of gods to protect their heads from bird droppings.
Investigating the function of the original circular halo in religious art only takes us back as far as the 1st Century BC. It had not featured in any prior religion, and yet it became a fixed piece of religious iconography across Eurasia within a few centuries.
It is likely to have evolved from very early art traditions. In ancient Egypt, the solar deity Ra was commonly shown with a circular disc representing the sun – although this was above his head rather than behind it. Meanwhile, some artefacts from the city of Mohenjo-daro (in the Indus valley), created in the 2000s BC, feature what look like rayed auras. However, these are inscribed around the whole bodies of holy figures, rather than just their heads. Likewise in the art of ancient Greece there are occasional representations of rayed crowns of light surrounding the heads of mythological heroes to suggest their unique divine powers. But the distinctive circular disc halo is an invention of a later date and presumably the result of unique religious ideas.
The earliest examples of a disc halo come from the 300s BC in the religious art of ancient Iran. It seems to have been conceived as a distinguishing feature of Mithra, deity of light in the Zoroastrian religion.
And how did it become a part of Christianity?
With the growing acceptance of Christianity in the Roman Empire, artists began to represent Jesus with a halo, now regarded as the highest symbol of divinely sanctioned authority. This new arrival in Christian iconography occurred from around the 300s AD, more than two centuries after it had appeared in Buddhism. It was a signal of Christianity’s metamorphosis from a marginalised religion to an official power structure in the west.
The halo has stuck in Christian art ever since, although it has undergone some adaptation over the years. God the Father can sometimes be seen crowned with a triangular halo, Jesus a cross-shaped halo and living saints a square halo.
