On December 2013, the town of Montescaglioso (Basilicata, Southern Italy), located at the top of a prominent hill within a highly landslide-prone setting, was affected by reactivation of a large earth-slide along the south-western slope. The slope is formed of stiff clays, belonging to the Argille Sub-appennine formation, covered by sands and conglomerates, with these latter being chaotically dislocated into arenaceous blocks resulting from ancient gravitational processes. The sliding movement started rapidly, accordingly to eyewitness accounts, and in a time span lower than 1 hour destroyed more than 500 m of the main road connecting the town of Montescaglioso to the Province Road SP175, and involved a few warehouses, a supermarket, and private homes. Surface displacement analysis jointly with detailed field surveys, and with visual analysis of post-event terrestrial and helicopter-based photographs, carried out soon afterward the landslide activation, allowed to identify the main effects produced by the slope movement, and to compile a map of the landslide surface deformations, aimed at identifying the landslide zones characterized by different kinematical features. Both geomorphological evidences and post-event inclinometric measurements have indicated that the failure surface has presumably developed at high depths and specifically in the clay substratum. Laboratory tests have been carried out for the characterization of the mechanical behavior of the clays involved in the sliding process. Both a two-dimensional and a three-dimensional finite element analysis were carried out in order to investigate the overall failure mechanism, the factors that could have controlled the landslide triggering and the spatial directivity of the landslide movement. The modeling results are in very good agreement with the observed landslide process as regards the conditions leading to the slope reactivation and the displacement field occurred in situ and highlight the role of the slope saturation as the main triggering factor of the landslide process.