The matter of long-term stability of long, natural slopes in illitic clay is of great practical importance in Scandinavia and Canada and has been frequently discussed among geotechnical specialists. A remaining question is how such natural slopes can have remained stable, yet undergoing large strain, for hundreds and thousands of years, during which critical conditions have repeatedly occurred with calculated safety factors lower than or equal to unity according to common stability calculations based on plastic theory. The reason for this may be the role of creep shear strain that causes redistribution of stress and earth pressure leading to a state of equilibrium that is very sensitive to disturbance and represents a condition of near-failure. Triggering of occasional slides can be explained by temporary high porewater pressure caused by periods of intense rain, disturbance by pile driving, or loading by road construction etc, taken place in slopes that have been stable for very long periods of time. The mechanisms by which creep can lead to stable conditions of very old clay slopes can have the form of successive relative particle movements into a state where the interparticle bonds become stronger but of brittle character, according to a model based on stochastical mechanics.