Quetta and Mehrgarh area in the vicinity of the Bolan pass, are being
  treated as signs of a foreign infiltration towards the end of the Indus
  civilisation.
  The advocates of this view ignore the facts that these objects may well
  have belonged to the mature Harappan period and that such finds in the
  Oxus-Indus interaction zone are only to be expected in view of the close
  trading network all over the interaction area.
  There is no evidence of any Aryan invasion or infiltration, causing the
  flight of the Harappans. The source of this error is the European scholars’
  inability to correctly interpret Sanskrit and local languages. So what
  happened to the Harappans?
Process and Nature of Decline
Degeneration in Late Harappan Phase Hence, the decline and
transformation of the Indus civilisation has to be understood in its own terms,
and it is here that we have to focus closely on archaeological stratigraphy and
the changing cultural situation, to which attention has been drawn long ago in
the context of Sind.
     • The idea of a degenerate Late Harappan Phase was first put forward in
         the context of pottery found in the upper levels of two sites in Sind,
         Jhukar and Lohumjodaro. Certain ceramic changes were taking place
         towards the stratigraphically upper or late phase of the Indus
         civilisation.
     • The brick masonry of Mohenjodaro during its late period, was poor
         by the standard of the earlier periods, and towards the end of the Late
         Period, a particular excavated area came to contain potters’ kilns,
         including one in the middle of its main street. That the potters could
         set up kilns in an area which was purely residential before, was an
         indication that the civic standard had remarkably declined during this
         period.
     • The same point has been highlighted by the current excavations at
         Harappa. Overcrowding of the site has also been noted here towards
         the late phase. The period which has specifically been called Late
         Harappan is Period 5, characterised        by a pottery known as Cemetery