[James C. Bennett]

If they could figure out trans-national trade, construction of rectangularly-laid city blocks and indoor plumbing made of fired clay components, they probably knew how to read and write:

Indus bath / pool ruins:

Indus sewage system (cover tiles removed):

Indus trade seal:

 

Indus map:

 

Time period: Circa 3300 BC to Circa 1300 BC.

[SunkenCiv]

The pools are interesting, in that they also are found (of much more recent construction, for the most part) in the Maldives.

[Ciexyz]

Lovely artwork on the seal.