With the help of archaeological excavations, radiocarbon dates have been collected showing that people first settled at Djenne-Jeno permanently in about 250 B.C. This first occupation of the site (which lasted from 250 B.C. to A.D. 50) is known as Phase I and is some of the earliest evidence for iron production in sub-Saharan Africa. This initial phase is not associated with the Later Stone Age, and there has never been an occupation from this period at the site, or evidence for it has never been found. Until 250 B.C., the area surrounding Djenné-Djenno was either uninhabited or visited by nomadic groups that stayed for short periods. Geomorphological data show that the region consisted mostly of swampland at that time. Groups only began permanently occupying the area after a dry episode in which annual flooding receded and decreased the size of the swamps. Faunal remains at the site from this occupation have included catfish and Nile perch but mostly cow, leading to the assumption that this first phase might be associated with hunter-gatherer or pastoral modes of subsistence. During this period there is no evidence for rice production, however it is believed that these people might have been rice producers, even though no definitive evidence has been discovered yet.