Islam categorises reality into two clearly separated spheres; lay and sacred. This division determines nearly every sphere of the Muslim's life. Because of the importance of this division, sanctified by religion and custom, borderline places, which both link and separate both worlds, become particularly important. The author discusses the problem of border as one of the most basic issues of the culture. He analyses it in the context of the rural environment of Northern Sudan, which he learnt during his two study trips. In Northern Sudan it is the Nile that serves as the physical and symbolic border area. It is most strongly associated with the experience of border and sacrum. Because of this, it is a model of the conceptualisation of all kinds of places or events, which give the impression of border crossing. The phenomena described in the article, although strongly connected with the North Sudanese context, are basically common to the other areas of the Middle East. Simply, because they are integrally linked to Islam.