The systematic urban layout of the mature Harappan cities (about 2600 to 1900 BCE), marked by a grid pattern, an upper citadel and a lower town, standardised bricks and an advanced drainage system, the hallmark of India's first urbanisation.
- Cities had two parts: a raised citadel (the western mound, holding public buildings) and a lower town to the east (residential and commercial).
- Streets ran on a grid, cutting each other at right angles, with main roads up to several metres wide.
- Burnt bricks were used in a fixed ratio (length to breadth to thickness of 4:2:1), showing standardisation across distant sites.
- An elaborate covered drainage system ran along the streets, with house drains connecting to street drains and soak pits; sanitation was a notable feature.
- Public structures: the Great Bath at Mohenjodaro (a watertight tank, probably for ritual bathing) and granaries at Harappa and Mohenjodaro.
- There were no large temples or palaces of the kind seen in Mesopotamia or Egypt, suggesting a different, perhaps merchant-led, social order.
The grid plan, citadel and lower town, the 4:2:1 brick ratio, the drainage and the Great Bath are among the most repeated Harappan features, often contrasted with Mesopotamian city patterns.
The citadel is the western raised mound, the lower town the eastern residential area; the absence of grand temples and palaces distinguishes Harappan cities from contemporary Mesopotamian and Egyptian ones; the standard brick ratio is 4:2:1.
Grid streets, citadel plus lower town, standard 4:2:1 bricks, covered drains and the Great Bath, the signs of India's first urbanism.