"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.
Even if one is interested only in one's own society, which is one's prerogative, one can understand that society much better by comparing it with others.