Settlements were scattered across the island in small clusters of peasant huts with crops grown in open fields. Social activities were centred around separate ceremonial centres, which were occupied for part of the year. The chief monuments were large stone platforms, similar to those found in other parts of Polynesia and known as ahu, which were used for burials, ancestor worship and to commemorate past clan chiefs. What made Easter Island different was that crop production took very little effort and therefore there was plenty of free time which the clan chiefs were able to direct into ceremonial activities. The result was the creation of the most advanced of all the Polynesian societies and one of the most complex in the world for its limited resource base. The Easter Islanders engaged in elaborate rituals and monument construction. Some of the ceremonies involved recitation from the only known Polynesian form of writing called rongorongo, which was probably less a true script and more a series of mnemonic devices. One set of elaborate rituals was based on the bird cult at Orongo, where there are the remains of forty-seven special houses together with numerous platforms and a series of high-relief rock carvings. The crucial centres of ceremonial activity were the ahu. Over 300 of these platforms were constructed on the island, mainly near the coast. The level of intellectual achievement of at least some parts of Easter Island society can be judged by the fact that a number of these ahu have sophisticated astronomical alignments, usually towards one of the solstices or the equinox. At each site they erected between one and fifteen of the huge stone statues that survive today as a unique memorial to the vanished Easter Island society. It is these statues which took up immense amounts of peasant labour. The statues were carved, using only obsidian stone tools, at the quarry at Rano Raraku. They were fashioned to represent in a highly stylised form a male head and torso. On top of the head was placed a 'topknot' of red stone weighing about ten tons from another quarry. The carving was a time-consuming rather than a complex task. The most challenging problem was to transport the statues, each some twenty feet in length and weighing several tens of tons, across the island and the then erect them on top of the ahu.
The Easter Islanders' solution to the problem of transport provides the key to the subsequent fate of their whole society. Lacking any draught animals they had to rely on human power to drag the statues across the island using tree trunks as rollers. The population of the island grew steadily from the original small group in the fifth century to about 7,000 at its peak in 1550. Over time the number of clan groups would have increased and also the competition between them. By the sixteenth century hundreds of ahu had been constructed and with them over 600 of the huge stone statues. Then, when the society was at its peak, it suddenly collapsed leaving over half the statues only partially completed around Rano Raraku quarry. The cause of the collapse and the key to understanding the 'mysteries' of Easter Island was massive environmental degradation brought on by deforestation of the whole island.