The Pyramid of Giza (the largest one) was beleived to have been built over a 20 year period finishing around 2560 BC. It had been the tallest man made structure for 4300 years. It is made entirley out of limestone and contains around 1 300 000 blocks ranging in weight from 2.5 tons to 15 tons. The amazing part of this is that no machinery existed in those days and every block of limestone was carved out of the ground and dragged by man who raised the blocks higher as they built upwards.