Indus Valley Civilization’s Collapse Explained

http://en.wikipedia.org/wiki/Indus_script

is a writing system at all, rather than the kind of ornamentation from a pre-proto-writing stage known in several other sites of ancient civilizations. (As a reality check, we can remember that several regions of the world had elaborate empires and cities with extensive trade routes but without writing.)

Some of the controversy about this issue arises because of the extreme sensitivity of cultural heritage claims in south Asia in a region that spans a heavily militarized border. A good popular book about the nature and origin of writing systems in general, worldwide, is Visible Speech by John DeFrancis,

http://www.amazon.com/Visible-Speech-Diverse-Interactions-Co...

and the definitive compilation of international research on writing systems to the date of publication is The World's Writing Systems

http://www.amazon.com/Worlds-Writing-Systems-Peter-Daniels/d...

edited by Peter T. Daniels and William Bright and published in 1996. I haven't concluded absolutely that the Indus Valley Script could not be a writing system, but there is no sure evidence that it is, and the earliest attested writing system in a nearby region is the Brahmi script

http://en.wikipedia.org/wiki/Br%C4%81hm%C4%AB_script

that is much more recent in time (a few centuries older than the common era, that is approximately 2,300 years old) and unquestionably based on the scripts of the ancient Near East.

It's amazing how quite advanced technologies (for a civilization that thrived from 5000 to 3000 years ago) were mastered only to be lost later over the course of history.

A mind-blowing example closer to us is the Antikythera mechanism [1]. Found in a Mediterranean wreck in 1900, the artifact was not analyzed until the 1950s, when it was found to be "a mechanical computer designed to calculate astronomical positions" - except it was made in the first century BC.

Wikipedia notes that "Technological artifacts of similar complexity and workmanship did not reappear until the 14th century, when mechanical astronomical clocks were built in Europe."

It is the oldest known mechanical computer - and to my knowledge no comparable device was to be manufactured until the 17th century and the invention of the Pascaline [2]. That's 18 centuries of gap, right there.

The precision of the clockwork and the exactitude of the astronomical calculations made by the Antikythera mechanism only goes to show how much knowledge was lost in Europe after the fall of the Roman Empire. Progress does not always follow a straight arrow.

[1] http://en.wikipedia.org/wiki/Antikythera_mechanism

[2] http://en.wikipedia.org/wiki/Pascaline