"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.
I'm chairing a UNESCO committee on how to improve global Internet communications for science help third-world people get onto the Net so they can be part of the process.