List me down some key aspects about windmills from given text.
1. Before 9th century there is no evidence of Windmills.
2. In first century roman Egypt , Heron described what is wind driven wheel to power machine.
3. As per the description given by him the wind-powered organ was either an early wind-powered
toy or a design concept for a wind-powered machine that may or may not have been a working
instrument.
4. One more early example(either the 7th century, or after the 9th century) of a wind-driven wheel
was the prayer wheel, which was first used in Tibet and China.