PYRAMIDS

Mind-blowing facts about the world's most enigmatic structures:

1. They are aligned to the true north with incredible accuracy. The Great Pyramid is just 3.4 arcminutes off perfect alignment or precision of ~1 millimeter per meter of the length of its base.

2. The Great Pyramid was the tallest building in the world for around 3,800 years until it was surpassed by Lincoln Cathedral in the 14th century.

3. They do not contain any hieroglyphs or paintings, nor were any burial treasures or mummies found within. By contrast, the tombs at the Valley of the Kings are decorated with intricate hieroglyphic texts and artworks from floor to ceiling.

4. They were once covered in gleaming white limestone casing stones (as pictured). Some researchers also think the capstones at the top were plated with precious metals.

5. ~2.3 million stone blocks make up the Great Pyramid, averaging 2.5 tons in weight. Quarrying these with little else than copper saws, chisels, and pounding stones, then transporting and lifting them into place, is the most remarkable engineering feat ever accomplished.

6. The casing stones and inner chamber blocks of the Great Pyramid were fitted together with such high precision that a knife's edge could not fit between them.

7. The Great Pyramid weighs nearly 6 million tons in total. Today, the only structures exceeding this are the Great Wall of China and the Three Gorges Dam.

8. When Napoleon visited the Great Pyramid in the late 18th century, he correctly calculated that it contained enough material for a 10-foot-high wall around the entire perimeter of mainland France.

9. Of the thousands of hieroglyphs found across Egypt, none of them mention how the pyramids were built or how the Egyptians cut stone. There are very few ancient Egyptian texts that mention the pyramids at all.