How many years did it take to build the Taj Mahal?

How to get close to this number

Estimate from the scale and the technology. A monumental marble structure with extensive inlay, built with hand tools and animal transport, takes decades rather than years. Two decades is the typical span for a major pre-industrial monument, and the Sagrada Família question on this site shows what happens when funding rather than technique is the constraint.

The workforce figures in the explanation make the schedule comprehensible: around twenty thousand workers and a thousand elephants. That is an industrial operation by pre-industrial means, and it is the only way a structure of this precision gets finished within one ruler's reign rather than across generations.

The ending is the detail that gives the monument its character: it was built as a tomb for one woman by an emperor who was later imprisoned by his own son within sight of it. A building intended as an act of permanent devotion became, for its patron, a view from a cell — which is a better summary of dynastic politics than any date.