An excavation across the Himalayan Frontal Thrust near Damak in eastern Nepal shows displacement on a fault plane dipping ~22° has produced vertical separation across a scarp equal to 5.5 m. Stratigraphic, structural, geometrical, and radiocarbon observations are interpreted to indicate that the displacement is the result of a single earthquake of 11.3 ± 3.5 m of dip‐slip displacement that occurred 1146–1256 A.D. Empirical scaling laws indicate that thrust earthquakes characterized by average displacements of this size may produce rupture lengths of 450 to >800 km and moment magnitudes M_w of 8.6 to >9. Sufficient strain has accumulated along this portion of the Himalayan arc during the roughly 800 years since the 1146–1256 A.D. earthquake to produce another earthquake displacement of similar size.