"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.
We can safely abandon the doctrine of the eighties, namely that the rich were not working because they had too little money, the poor because they had much.