Despite almost a century and a half of excavation, the dynamic landscape into which the temple complex of Karnak was embedded is not well understood. Presenting the results of the first comprehensive geoarchaeological survey of the area, the authors show that Karnak was built upon a fluvial terrace segment surrounded by river channels in an island configuration potentially recalling the ‘primeval mound’ of Egyptian creation myths. Permanent occupation of the site became possible after 2520 BC ±420 years, likely during the Old Kingdom. Subsequent landscape changes were dramatic, with the occupants of the island responding both opportunistically and proactively.