"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.
With everything that is complex, we learn. If you don't learn, then it's an utter and abject failure. If you do learn, and you're able to apply that to the next situation, then you take away a measure of success.
The point in history at which we stand is full of promise and danger. The world will either move forward toward unity and widely shared prosperity - or it will move apart.