History : 5 things you didn't know about pyramids of Giza

1. The pyramid is estimated to have around 2,300,000 stone blocks that weigh from 2 to 30 tons each and there are even some blocks that weigh over 50 tons.
2. The interior temperature is constant and equals the average temperature of the earth, 20 Degrees Celsius.
3. The four faces of the pyramid are slightly concave, the only pyramid to have been built this way.
4. The curvature designed into the faces of the pyramid exactly matches the radius of the earth.  
5. The cornerstone foundations of the pyramid have ball and socket construction capable of dealing with heat expansion and earthquakes.