"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.
You can't write about the past and ignore religion. It was such a fundamental, mind-shaping, driving force for pre-modern societies. I'm very interested in what religion does to us - its capacity to create love and empathy or hatred and violence.