The legends of Easter Island say that Hotu Matua came first came ashore here at Anakena Beach and that this was the island's first settlement. Excavations of the site have confirmed that it had been occupied for a very long time. The current ahu is built upon the remains of several others and the same precise stone work is found in the buried ahu as that of Ahu Vinapu. Again, this is curious because one would expect the more advanced stonework work have been done during later periods of the island's development.
What is striking about the statues at Ahu Naunau are the red scoria headdress's (known as Pukao) that fit on the moai heads. These were carved from a different quarry than those of the moai that contained a large quantities of the red lava rock. Many of the moai on the island originally had pukao and they are found alongside the fallen statues in many sites. It is believe that they where installed by building a ramp of stones up the side of an erected moai and then rolled up where they could be placed on the top. Afterwards the ramp was disassembled.
Reference: http://www.mysteriousplaces.com/Easter_Island/html/site5.html