Compelling physical evidence for a Late Aptian lowstand with an amplitude of at least 50m is presented in subsurface seismic and core data from the Arabian Plate. Biostratigraphic dating indicates that the fall and rise bracketing this lowstand were rapid, and that the lowstand lasted for around 5ma with distinctly cyclic sedimentation at the 0.4-0.5ma scale (eccentricity band). A glacio-eustatic mechanism is invoked as the most likely cause, which is supported by cooling indicated in oxygen isotope shifts and by evidence for a global expression of this lowstand from a number of locations at the mid and high latitudes. Hence, the Late Aptian data presented here document the longest Cretaceous sea-level lowstand, interpreted as the longest cooling phase during the Cretaceous greenhouse. © 2012 Blackwell Publishing Ltd.