A procedure incorporating geological evidence with analytical methods was developed for the back analysis of a multiple retrogressive landslide in Cretaceous clay shale. The slide mass, apparently inactive, extends 2 km back from the toe at the river and is seated on a shear zone 100 m deep at the main scarp. Historical evidence of the slope movement was established from radiocarbon dating of the river alluvium over which the landslide moved. The geometry of the landslide when the factor of safety was near unity was determined from historic and stratigraphic evidence and sensitivity analyses.The stratigraphy of the slide mass showed that the beds are stretched with very little vertical displacement, indicating a mainly translational mechanism along a nearly horizontal shear zone. Apparently movement has taken place at a slow but steady rate over 11 000 years, resulting in a horizontal displacement of 390–430 m at the toe. The landslide, therefore, was analyzed as a series of sliding blocks with a common failure surface retrogressing from the toe up to the scarp. Each successive block was combined and considered to be moving as a single unit. Unknown factors, such as pore-water pressure at failure and the influence of cohesion, were evaluated by sensitivity analyses. The effective angle of shearing resistance required for limiting equilibrium was relatively constant, ranging from 7.6 to 8.7°, assuming the water table to be near the ground surface. For a lower water table, the values ranged from 6.5 to 8.0°. The equivalent values of cohesion required for equilibrium withranged from 42 to 82 kPa depending on the size of the block, suggesting thatc′ must be zero for the retrogressive mechanism analyzed by combining successive blocks.Keywords: slope stability, multiple-block, back analysis, residual strength, sensitivity analysis.