Interesting fact:

Ten football fields can be covered by the base of the Great Pyramid of Giza in Egypt. The pyramid is the oldest of the Seven Wonders of the Ancient World, and at 481 ft (146.5 m) was the tallest man-made structure in the world for more than 3,800 years. The Greek historian Herodotus wrote that it took 400,000 men twenty years to build this great monument, which consists of approximately 2.3 million blocks!