7 Wonders
The Great Wall is more than 21,000 kilometres long
A 2012 survey counted all branches and eras of construction at 21,196 km. It is not one continuous wall but many walls built by different dynasties over 2,000 years.
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Only one ancient wonder is still standing
The Great Pyramid of Giza is the sole survivor of the seven wonders of the ancient world. It was already more than 2,000 years old when the original list was compiled.
The Great Pyramid held a record for 3,800 years
At 146 metres, it was the tallest human-made structure on earth from about 2560 BC until Lincoln Cathedral's spire was completed around 1311 AD.
The pyramid is aligned almost perfectly to north
Its sides face the cardinal directions to within a fraction of a degree, an accuracy achieved without compasses, most likely by tracking stars circling the celestial pole.
Nobody has ever found the Hanging Gardens
Ancient writers described terraced gardens watered by machinery in Babylon, yet no Babylonian text or ruin confirms them. Some scholars argue the gardens were actually in Nineveh.
Watering the gardens needed serious engineering
Lifting river water up terraces in a desert climate would have required chain pumps or an Archimedes-style screw, technology described centuries before Archimedes was born.
The statue of Zeus was 12 metres of gold and ivory
Made by Phidias around 435 BC at Olympia, the seated Zeus nearly touched the temple ceiling. Visitors joked that if he stood, he would take the roof off.