In the Sigatoka Valley on Viti Levu Island in Fiji, three independent studies of last-millennium environmental and human-societal changes suggest that these were driven largely by the climate and sea-level changes of the AD 1300 Event. Establishment dates for interior fortified hilltop (or cave) settlements show that a significant number were established during or shortly after the AD 1300 Event, probably in response to primarily food shortages arising from sea-level fall (affecting coastal populations) and water-table fall (affecting coastal and inland populations). Charcoal concentrations in valley-floor sediments formed as a result of largely human burning of vegetation associated with the establishment of inland hilltop settlements; radiocarbon dates from these charcoals also suggest significant numbers of such settlements being established during or shortly after the AD 1300 Event. The main dune at the Sigatoka River mouth is underlain by the 'Level 3' palaeosol, dated to the AD 1300 Event, which implies that thereafter an abrupt and sustained increase in suspended fluvial sediment, associated in increased inland population, began to build the high dunes visible today. This study provides a well-constrained example of the effects that the AD 1300 Event had on Pacific Islands and their people.