Forbidden City builders chose ice sledge over wheels

Fifteenth-century Chinese engineers didn't so much reinvent the wheel as dispense with it altogether – opting to drag heavy stones for building the Forbidden City along a slippery artificial ice road instead of wheeling them.

That, at least, is the upshot of the latest analysis of a 17th-century Chinese text. Such a method would be 10 times as efficient as dragging the rocks along non-icy ground – suggesting that Chinese engineers had a more sophisticated understanding of friction than their Western counterparts at that time.

The Forbidden City, in what is now Beijing, housed China's emperors for almost 500 years. Several of the massive stones incorporated into its design were extracted from the Dashiwo quarry. That is 70 kilometres away – and the stones weigh in excess of 100 tonnes....