The first Fort William, near what is now the GPO, fell to Siraj-ud-Daulah in June 1756. After Plassey the Company built a second one, further south, on a scale that assumed it would have to hold against a European army.
It is an irregular octagon on the Vauban system, with five landward bastions and three facing the river, a wet ditch, and glacis on every side. Construction ran from 1758 to 1781 and cost around two million pounds, which was an enormous sum and remains the most expensive thing the Company built in India.
To give the guns a clear field of fire the Company cleared the jungle and the village of Gobindapur around it. That clearing was never built on, and it is the Maidan: roughly a thousand acres of open ground in the middle of the city, which exists entirely as a side effect of artillery ranges.
It was never attacked. It is now the headquarters of the Indian Army's Eastern Command and closed to the public. The star plan is legible from the air and from nowhere on the ground.
What the guidebook leaves out
The Maidan is the fort's field of fire. The largest open space in any Indian city exists because of a sightline for cannon that were never fired.
