Purana Qila, situated on the banks of Yamuna, is associated with Mughal emperor Humayun. It is where Humayun's capital Din Panah was located. Later it was renovated and named Shergarh by first Afghan emperor of India, Sher Shah Suri.
Sher Shah Suri defeated Humayun in 1540, and renamed the fort as Shergarh, and also added several more structures in the complex, during his reign that lasted for the next five years until his death in 1545.
Subsequently Islam Shah took over the reigns of North India from this fort, but later shifted his capital to Gwalior, as it was supposed to be a safer capital in that period. After Islam Shah's death in 1553, Adil Shah took the charge of North India, and this fort remained neglected. Adil Shah shifted his capital to further east to Chunar in present day Uttar Pradesh. Humayun, who was based in Kabul got an opportunity to re-capture the citadel and the seat of Delhi in 1555, fifteen year after he had to leave it, though his reign didn't last long, he died only a year later in Jan. 1556, due to a tragic accident, within the fort complex at Sher Mandal.
Hearing about re-capture of Delhi by Humanyun, Hemu, the Hindu Prime Minister - cum - Chief of Army of Adil Shah rushed towards Delhi from Bengal, where he had just quelled a rebellian, defeating and killing Muhhamad Shah, the ruler of Bengal. After capturing Agra, Itawah, Kanpur easily, the battle for Delhi took place in Tuglakabad area on 6th Oct. 1556, and Hemu, who had won 22 battles spanning entire north India, defeated the forces of Akbar which were lead by Tardi Beg Khan. Hemu had his'Rajyabhishake' or Coronation at Purana Quila on 7th Oct. 1556, declared'Hindu Raj' in North India, and was bestowed the title of Samrat Hem Chandra Vikramaditya. Hemu, who was slain and killed at the Second battle of Panipat in Nov. 1556 had his torsoe hung outside this fort to creat terror among Hindus.
The walls of the Fort rise to a height of 18 mtrs., and run on for about 1.5 km, and has three arched gateways, the Bara Darwaza (Big Gate) facing West, which is still used today, the south gate, the'Humayun Gate' probably called so because it was constructed by Humayun or that Humayun's Tomb is visible from there, and lastly, the'Talaqi Gate' or forbidden gate. All the gates are double-storeyed sandstone structures flanked by two huge semi-circular bastion towers, and decorated with white and coloured-marble inlays and blue tiles, and replete with detailing, like ornate overhanging balconies, jharokhas, pillared pavilions chhatris on top, reminiscent of Rajasthani architecture as seen in the North and South Gates, and which were amply seen in future Mughal architecture. Despite the grandeurs of the exterior, few of interior structures have survived except the Qila-i Kuhna Mosque and the Shermandal, both credited to Sher Shah.