One of Kolkata's most enduring British-era military fortifications, other than those in Bombay (Mumbai) and Madras (Chennai), it extends over an area of seventy hectares.

The original fort was built in the year 1696 by the British East India Company under the orders of Sir John Goldsborough which took a decade to complete.

[2][3] Sir Charles Eyre started construction near the bank of the Hooghly River with the South-East Bastion and the adjacent walls.

In 1756, the Nawab of Bengal, Siraj Ud Daulah, attacked the Fort, temporarily conquered the city, and changed its name to Alinagar.

Robert Clive started rebuilding the fort in 1758, after the Battle of Plassey (1757); construction was completed in 1781 at a cost of approximately two million pounds.

[4] Much of Fort William is unchanged, but St Peter's Church, which used to serve as a chaplaincy centre for the British citizens of Kolkata, is now a library for the troops of HQ Eastern Command.

The design is that of a star fort, suited to defence against cannon firing solid shot, and dates from before the advent of explosive shells.