 They are associated with the Latte period (900 to 1700 CE), when a new wave of migrants from Southeast Asia reintroduced rice cultivation into the islands.Another megalithic tradition is also that of the rai stones, massive doughnut-shaped discs of rock which were used as currency in Yap.Rock art in central Micronesia (Chuuk, Pohnpei, and Kosrae), in contrast, are dominated by rock engravings with motifs tying it to the rock art traditions of Island Melanesia.