While the term arching has been accepted in the geotechnical literature, the concept does not relate to a formation of a physical arch (as seen in karst formations), but rather a re-distribution of stress (or variation in the stress field), where stiffer components of the system attract more loads. The description is still elusive, and research toward prediction of arching is carried out. Arching in a model of a sand heap is illustrated in the figure, producing a stress ‘dip’ at the center of the base. The significance of this phenomenon was probably overstated in the Science article of Watson (1996): “… sand pile pressure dip is to granular mechanics what Fermat’s Last Theorem was to number theory.” While the appearance of the stress dip may be a curiosity problem, arching associated with it is a phenomenon of interest and importance in geotechnical engineering.