During the late period of this civilisation, signs of a gradual decline began to emerge, and by around 1700 BCE, most of the cities were abandoned. However, the Indus Valley Civilisation did not disappear suddenly, and some elements of the Indus Civilisation may have survived. Aridification of this region during the 3rd millennium BCE may have been the initial spur for the urbanisation associated with the civilisation, but eventually also reduced the water supply enough to cause the civilisation's demise, and to scatter its population eastward. The civilization collapsed around 1700 BCE, though the reasons behind its fall are still unknown. Through the excavation of the Indus cities and analysis of town planning and seals, it has been inferred that the Civilization had high level of sophistication in its town planning, arts, crafts, and trade.