"Ahu" are stone platforms on which many moai sit. There are 313 known ahu and 125 of these carry moai. The biggest, Ahu Tongariki is 220 m (720 ft), and had the most (15) and tallest moai.
To demonstrate that speed of descent is independent of an object's mass Galileo Galilei is said to have dropped two cannonballs of differing mass from the tower. However, this is believed to be an old wives' tale.
