Dockyard was found at which of the following Indus Valley Civilisation cities?

Concept: Every major Harappan site is identified by the signature structure its excavation revealed. A great bathing tank and a granary mark the largest citadel cities; a massive stone fortification wall marks a frontier outpost at the edge of the culture; and a dockyard — a large baked-brick tidal basin fitted with an inlet channel and a sluice or spill-way so that boats can be berthed and floated out again — marks a coastal or estuarine settlement that handled sea-borne trade. A site-feature question is therefore answered by matching the named structure to the excavation report that recorded it.

Application: The tidal basin answering that description was uncovered at Lothal, in the Bhal region of Gujarat, on the Bhogavo river a short way inland from the Gulf of Khambhat.

• Excavation. Lothal was excavated for the Archaeological Survey of India by S. R. Rao between 1955 and 1962.

• The structure. On the eastern flank of the settlement lies a trapezoidal basin lined with baked brick, roughly 214 m long, 36 m wide and about 3.3 m deep — far larger and far more carefully water-proofed than any domestic tank or reservoir at the site.

• The water works. An inlet channel led river water into the basin and a spill-way with a sluice arrangement held the level up, so that vessels stayed afloat when the tide outside fell. It is this inlet-plus-sluice combination, not the size alone, that identifies the basin as a berthing structure rather than a reservoir.

• The supporting finds. A brick warehouse on a raised platform stands beside the basin, together with a bead-making workshop and a circular Persian Gulf-type seal — the material signature of a settlement trading by sea with Mesopotamia.

Cross-check: Each of the other Harappan sites named in the question is known for a completely different signature feature, so none of them competes for this description:

Result: The dockyard of the Indus Valley Civilisation was found at Lothal.