"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.
The economic interpretation of history does not necessarily mean that all events are determined solely by economic forces. It simply means that economic facts are the ever recurring decisive forces, the chief points in the process of history.