Short answers, pulled from the story.
Hajiganj Fort was built to prevent Magh and Portuguese raids on Dhaka after Subahdar Islam Khan established the Mughal capital there. Along with Sonakanda Fort and Idrakpur Fort, it formed a coordinated river-based defence system for the city.
Hajiganj Fort is situated in the Hajiganj locality of Narayanganj, Bangladesh, on the western bank of the Shitalakshya river. Its historical name, along with the surrounding area, was Khizirpur.
Hajiganj Fort features a quadrangular layout with a pentagonal curtain wall, rounded corner bastions, and a machicolated parapet. The rampart walkway is elevated 1.22 meters from the base, with merlons designed for cannon fire and musketry holes for handheld firearms. A freestanding tall square brick column in one corner likely served as a guard tower.
Islam Khan used Hajiganj Fort considerably in assaults against the Baro-Bhuiyans, local chieftains who resisted Mughal authority. The fort also served as a defensive position to intercept river raiders threatening Dhaka.
The absence of permanent interior structures suggests Hajiganj Fort was primarily occupied during the rainy season, when pirate activity was anticipated, with occupants likely using tents for shelter. The seasonal flood-driven mobility of raiders made a permanent garrison less necessary.
The fort's sole gateway is positioned on the river-facing side. It is pentagonal in form, set within a rectangular structure with engraved rectangular arches on both sides, and crowned by a lotus finial.