A new non-destructive and readily applicable technique for measuring roughness of stone surfaces is presented here. The technique makes it possible to document quantitatively the present state of decay and to reconstruct the process of stone deterioration in past decades. The first measurements made in the Munich vicinity resulted in the following conclusions. By measuring the roughness it is possible to quantify the specific susceptibility or resistance to decay of various building stones under given weathering processes. In the new Nordfriedhof area, surface decay in the last 20-50 years did not increase progressively but continuously. Decay of stone surfaces exposed to rain and wind is greater than decay of protected surfaces. Even after a few years, measurable roughness profiles were formed with significant weathering back of the stone surfaces, especially on the margin of the capillary water fringe. Extrapolated to a millennium, the roughness progress of a stone surface amounts to one up to several millimeters. -- AATA