Most people don't realize how mysterious the Pyramids truly are

They're so old that Cleopatra lived closer to us than to their construction — yet Khufu's Pyramid is so precise it aligns north within 1/20th of a degree.

Some more mind-blowing facts about them… 

They're not just incredibly old, but impossibly precise.

The Great Pyramid (attributed to Khufu, c.2550 BC) is 3.4 arcminutes off perfect alignment with true north. That's precision of ~1 millimeter per meter of the length of its base.

Executing such accuracy on something with a 13 acre footprint is astounding — how did they do it?

Possibly with the help of the sun on the equinox, which on that day rises exactly in the east (and sets perfectly in the west)

Staying on precision, the inner chamber blocks of the Great Pyramid were cut and fit together so tightly that a razor blade cannot fit between them.

And some of the granite blocks of the King's chamber weigh 80 tons each.

Then there's the sheer scale: 2.3 million blocks make up the Great Pyramid, averaging 2.5 tons each.

Quarrying these with mere copper saws and pounding stones, transporting and lifting them into place, is a true enigma.

It's useful to compare it to the great constructions of our day. The Burj Khalifa may dwarf it in height, but a more telling measure is probably weight.

At 6 million tons, the Great Pyramid is 12x heavier than our greatest skyscraper.

But the Great Pyramid did hold the title of world's tallest building for 3,900 years — only surpassed in the 14th century by Lincoln Cathedral.

It was 481 feet tall, but erosion has reduced it slightly over time.

Once covered in limestone casing stones, they would've been majestic in their day. Some also think their capstones were plated with precious metals.

Both were likely plundered and repurposed following damages caused by a 14th century earthquake.

What's curious about the Giza Pyramids is that they do not contain a single hieroglyph or painting. Nor were burial treasures or mummies found inside.

That's clearly unusual for a tomb — other pyramids, like that of Unas, have protective spells etched into their burial chambers.

And by contrast, the tombs at the Valley of the Kings are decorated with intricate hieroglyphic texts and art from floor to ceiling.

These were meant to accompany the pharaohs on their greatest journey — into the afterlife.

In fact, only a handful of ancient texts have ever been found that even mention the Pyramids at all.

The best we have on their construction are these papyrus fragments, found in 2013, mentioning the delivery of limestone blocks via the Nile river.

Finally, the internal layout of the Great Pyramid is perplexing at best. These are tunnels of smooth rock without steps, all sloping 26 degrees (half that of the external walls).

There's even a giant, unexplored chamber yet to be found, according to recent imaging.

The list of questions goes on and on: why were mathematical constants encoded so carefully throughout, why were the internal slopes measured so precisely...

Advanced geometers and mathematicians were evidently at work here.

Struck by these vast achievements, it's interesting to ponder the societal organization that must have produced them.

Visiting in the 5th century BC, Herodotus supposed that some 100,000 men must have built them.

The Great Pyramid is usually attributed as a funerary monument to the Pharaoh Khufu — he was seen not just as an earthly ruler, but a divine one.

That the will of one man to live forever in stone could mobilize an entire population is daunting to imagine.

With all the looming questions, we can't say for sure exactly how or why they were built — but one thing is clear.

These structures were built to last forever.

These structures don't just fascinate modern observers. When Napoleon came in the 18th century, he correctly calculated that the Great Pyramid contained enough material for a 10-foot wall around the entire perimeter of France.

It's believed he calculated this himself.