"The Indus civilization has challenged scholars’ understanding since its discovery some eighty years ago, and in recent years the application of systematic and problem-orientated research, coupled with much new and unexpected data, has overturned many previous interpretations."

“The decline of Harappan urbanism probably had many contributing factors. The shift to a concentration on kharif cultivation in the outer regions of the state may have seriously disrupted established schedules for craft production, civic flood defense, building and drain maintenance, and other publicly organized works on which the smooth running of the state depended. The reduction in the waters of the Saraswati and the response of its farmers by migrating into regions to the east tore apart the previous unity of the Harappan state, disrupting its cohesion and its ability to control the internal distribution network.”

“In contrast, changes taking place in the Saraswati Valley in the early second millennium were probably a major contributor to the Indus decline. In Harappan times, the Saraswati was a major river system flowing from the Siwaliks at least to Bahawalpur, where it probably ended in a substantial inland delta. The ancient Saraswati River was fed by a series of small rivers that rose in the Siwaliks, but it drew the greater part of its waters from two much larger rivers rising high in the Himalayas: the Sutlej and the Yamuna. In its heyday the Saraswati appears to have supported the densest settlement and provided the greatest arable yields of any part of the Indus realms. The Yamuna, which supplied most of the water flowing in the Drishadvati, a major tributary of the Saraswati, changed its course, probably early in the second millennium, to flow into the Ganges drainage. The remaining flow in the Drishadvati became small and seasonal: Late Harappan sites in Bahawalpur are concentrated in the portion of the Sarawati east of Yazman, which was fed by the Sutlej. At a later date the Sutlej also changed its course and was captured by the Indus. These changes brought about massive depopulation of the Saraswati Valley, which by the end of the millennium was described as a place of potsherds and ruin mounds whose inhabitants had gone away. At the same time new settlements appeared in the regions to the south and east, in the upper Ganges-Yamuna doab. Some were located on the palaeochannels that mark the eastward shift of the Yamuna. Presumably many of the Late Harappan settlers had originated in the Saraswati Valley.”