Left panel: size (radius r) of 2207 boulders of the Imhotep region as a function of their gravitational slope angle θ (adapted from Auger et al. 2015). The black horizontal lines correspond to the angle of repose θ_repose = 45 ± 5°; there are no boulder on slopes larger than the angle of repose. Right panel: value rsinθ for each boulder, as a function of its radius. Both panels: for robustness, we rejected the upper 1% of the rsinθ distribution (blue points). For the remaining 99%, the boulder with the highest value rsinθ is highlighted in green and corresponds to r = 11.5 m and θ = 26.8°, as indicated by the green horizontal and vertical dashed lines.