The oil shale-deposits of the Messel pit have become famous through the discovery of superbly preserved vertebrate fossils of Eocene age and the controversial proposal about the after-use of the former open mine pit. Since 1995, when the Messel pit was placed on the UNESCO list of world heritage sites, especially the long-term safety of the artificial slopes is relevant for its future utilisation. The Messel pit is situated about 20 km south of Frankfurt am Main, Hesse, Germany, near the cities of Darmstadt, Dieburg and Langen. From 1885 to 1971 the oil shale of the Middle Messel-Formation was excavated by open-cast mining and crude oil was extracted in an associated plant until 1961. Slope failures already caused damages and losses of lives during the many years of open cast mining. Currently all slopes of the former open pit mine are considered as unstable. Because the Messel pit is operated as an opencast pit according to §52 of the federal mining law, the provincial government has taken over the responsibility for the site including possible health and safety issues. Therefore a geotechnical long-term monitoring of the slopes according to DIN 1054-100 is performed since 1993. As mentioned before, extensive slope deformations or sliding processes are presently pointed out for all of the artificial slopes. Mass movements of the Eocene sediments are limited by the marginal faults (detachment planes) of the Messel oil shale- deposit. Near the deposits border-area the deep-seated main sliding surfaces are predominantly located at the transition zone between the lower Messel-Formation and the oil shale of the Middle Messel-Formation. Towards the deposits centre where the dip of beds parallels the slope angle, these shear zones overlap to the oil shale of the Middle Messel-Formation, using its fine lamination as a sliding plane. Slope failures in the tertiary Messel-sediments are attributed to the complex concurrence of permanent factors such as development of stress respectively state of stress, characteristic material properties and joint system, provoking in combination the increase of shear stress, the contribution to low strength and the reduction of material strength. Unloading of the overcompacted sediments due to erosion and surface mining induced relaxation and development of lamination-parallel zones of weakness on which just the residual strength became operative and on which the slopes primarily failed. For normal status, measurement and monitoring indicates long-ranging small deformations for all landslides in the northern, eastern and south-western slope. Exceeding intense rainfalls may episodically trigger these slides to temporarily accelerated sliding. Considering monthly- and 72h-sum-intervalls of precipitation, qualitative stimulus thresholds were defined, whose exceedance accelerates deformations. The rapid infiltration of rainfall causes a temporary rise in pore-water pressures, hydrostatic joint-water pressures and an increasing softening of the shear zone material. These influences are generally supposed to be the primary mechanisms by which the slides are reactivated. The slope stability analysis demonstrated that according to DIN 1054-100 the required safety factors for loading case 2 (exceptional situation) and for loading case 1 (normal situation) are not ensured for any of the reactivated, suspended or dormant landslides. The required long- term safety of the artificial slopes is likewise not guaranteed. Small deformations will endure and episodic, temporary accelerations will occur every three to five years up to the achievement of stable slope-conditions. The identifiable risks for object and consequential damages resulting from slope instability are not tolerable. Taking into consideration a cost benefit analysis it seems adequate to reduce these risks by permanent control- and monitoring measurements according to the monitoring procedures of DIN 1054-100. Therefore a modified configuration for control- and monitoring measurements is introduced. Additionally, low priced local structural engineering measures leading to an increase of safety enhancement of vulnerable subareas are presented and recommended.