A 50–70 cm sea-level fall around a.d. 1300 may have led to a prolonged food crisis which caused conflict among coastal dwellers on high Pacific islands. The conflict may have necessitated abandoning difficult to defend coastal settlements and establishing ones in fortifiable locations inland. To test this idea, abandoned hillforts (koronivalu) on 20 km2 Yadua Island were studied. Yadua Island is 20 km off the western extremity of Vanua Levu Island, the second largest island in the Fiji archipelago, where many such hillforts once existed. Human-made structures (stone walls), artifacts (potsherds and lithics), and accumulations of edible seafood waste (shellfish middens), all implying sustained occupation, were identified at four sites in upland Yadua, including two hillforts (Koromakawa and Uluinakoro) and two lookout posts (Nacelau and Uluikota). Radiometric ages suggest the two hillforts were occupied during the seventeenth century or perhaps established earlier, making them coeval with hillforts elsewhere in Fiji and other tropical Pacific Island groups. Information about Pacific Islands settlement throughout the last millennium can still be obtained from islands like Yadua through fieldwork and the collection of oral traditions. Oral traditions and human-made structures are likely to disappear within a few decades, owing to the increasing reach of globalization and ongoing physical degradation respectively; research of the kind described in this article is thus a priority.