Short answers, pulled from the story.
Idrakpur Fort was established in 1660 during a crisis in the Mughal Empire when pirates from Portugal and Magh attacked wealthy cities like Sonargaon. Aurangzeb appointed Mir Muhammad Saeed Ardestani as Subahdar of Bengal that same year to protect the new capital at Dhaka from river-based raids.
Idrakpur Fort sits at the junction of the Ichhamati and Meghna Rivers while Sonakanda Fort stands on the eastern bank and Hajiganj Fort occupies the western bank. These three forts worked together to control waterways and prevent enemy vessels from advancing toward Dhaka.
The brick walls of Idrakpur Fort measure 86.87 meters long and 59.60 meters wide with bastions marking each corner. A circular drum rises 32.5 meters in diameter and 9.14 meters high within the eastern area surrounded by another wall designed to mount a massive cannon.
Mughal soldiers fired mortars from cannons on 200 battleships and from Idrakpur Fort when pirates advanced toward Dhaka. If any ships survived, Sonakanda and Hajiganj would fire round-shots to sink them creating a coordinated attack that left no escape route for enemy vessels.