New Delhi, Aug. 4 -- I have visited both Mohenjo-daro and Harappa, two of the great urban centres of the Indus Civilisation, located in present-day Pakistan. Standing among their brick ruins, I was struck by how much had survived in material form - and how much of the human life once lived there remains beyond our reach.

Years later, watching Omar Khan's documentary Mohenjo-daro: Unsealing an Ancient Indus City returned me to that tension - How much an ancient city can reveal, and how much it continues to withhold.

Bricks endure. Drains can be mapped. Seals can be catalogued. Metal objects can be preserved and displayed. We can trace evidence of trade, craftsmanship and organised urban life. However, it does not always tell us who perfo...