It is mentioned on the detail link for the chart: > Harappan Civilisation (Indus Valley Civilisation) [800] But also missing is the Sumerian civilization, whi

It is mentioned on the detail link for the chart: > Harappan Civilisation (Indus Valley Civilisation) [800] But also missing is the Sumerian civilization, which I understand to have been over a thousand years. https://en.wikipedia.org/wiki/Sumer https://en.wikipedia.org/wiki/Sumer