The Great Bath, Standard Weights, and a City-Wide Drainage System
Mohenjo-daro's engineers built a shared public bath and a metrology so precise it barely varied across 1,500 kilometers
Quick facts
- Great Bath location
- Citadel mound, Mohenjo-daro
- Waterproofing
- Layers of bitumen sealant
- Weights analyzed
- 558 stone weights from Mohenjo-daro, Harappa, and Chanhu-daro
- Weight ratio system
- Binary, approximately 1:2:4:8:16:32
What happened
At the center of Mohenjo-daro's citadel mound stands the Great Bath, a large brick-lined pool set in a courtyard with steps leading down on two sides, waterproofed with layers of bitumen. Its exact use is unknown, historian John Keay notes it may have served ritual purification or simply public bathing, but its presence at the settlement's highest and most prominent point suggests a shared civic or religious function rather than a private pool. Around it, Harappan cities ran covered drains along the main streets, connected to individual house latrines through a network more extensive than any comparable system built anywhere else at the time. Harappan merchants also used a standardized set of cubical stone weights: research on 558 weights recovered from Mohenjo-daro, Harappa, and Chanhu-daro found they follow a binary ratio system, roughly 1:2:4:8:16:32, with a base unit near 13.7 grams, and the values stayed statistically consistent across excavation layers spanning roughly 500 years.
Why it matters
A drainage network and a uniform weight system both require enforcement across many independent households and, at Harappan scale, across cities hundreds of miles apart. That kind of standardization does not happen without some form of shared authority or civic convention, even though the Indus script cannot yet tell us what that authority looked like.
How we know
The Great Bath and drains are standing excavated structures, first uncovered in the 1920s excavations at Mohenjo-daro. The weight standardization comes from statistical analysis of hundreds of recovered stone weights across three cities and multiple stratigraphic layers, published by Indus specialists working from the excavated collections.
Sources
- World History Encyclopedia. Indus Valley Civilization · Reputable sourceworldhistory.org · The domain "worldhistory.org" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- Harappa.com (J.M. Kenoyer, Harappa Archaeological Research Project). Cubical Weights · General sourceharappa.com · Cited as a "reference" source (no stronger domain match).
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