Saint Mark's in Venice and Ben Carson's take on the pyramids

Why do some people think the pyramids were grain stores?

I had no idea.

In the Old Testament, Joseph is sold into slavery in Egypt by his brothers, where he later interprets a pharaoh's dreams and helps the Egyptians survive a seven-year famine - by storing grain.

There is no mention of pyramids in the Bible's version of the story but in the Middle Ages people started to write them into the story.

"If you go to St Mark's cathedral in Venice, there's a medieval depiction showing people using the three great pyramids of Giza as granaries in Joseph's story," says John Darnell, a professor of Egyptology at Yale University.

"If you didn't have access to the structures, the idea had some currency."

The belief was also popularised by Saint Gregory of Tours, a sixth century Frankish bishop, who wrote: "They are wide at the base and narrow at the top in order that the wheat might be cast into them through a tiny opening, and these granaries are to be seen to the present day."

The Book of John Mandeville, a popular 14th Century travel memoir, also referred to "Joseph's Granaries, which he had made to store the wheat for hard times".

But Darnell says the idea began to fall out of favour during the Renaissance, when people made more detailed studies of the pyramids.