The paper presents the emblematic case of the Pianello slope, that is a complex landslide basin located in the town centre of Bovino, one of the most beautiful villages in Italy. The low gradient slope is formed of highly tectonised and heterogeneous clays and it is affected by very slow and deep landsliding. The failure mechanisms are representative of many others not only in the Daunia area in the south of Italy, but also in the slopes of the Italian Apennines. The analysis resulted from field surveys, investigations and monitoring data as well as from the laboratory test results of the geotechnical investigation. The phenomenological interpretation of the landslide mechanism, along with the identification of the predisposing and triggering factors has been validated by both limit equilibrium and numerical analyses.