Short answers, pulled from the story.
Purana Qila was built by the Mughal emperor Humayun, who began the city of Dinpanah on the site, and Sher Shah Suri, who defeated Humayun, strengthened the fortifications, and added a separate fort called Shergarh. The historical attribution remains disputed, as primary sources differ on how much each ruler completed.
Archaeological excavations led by B. B. Lal in 1954-55 and 1969-72 found Painted Grey Ware pottery dating to around 1000 BC beneath the fort. Later digs in 2013-14 and 2017-18 confirmed continuous occupation from the Mauryan through the Mughal period.
On the 24th of January 1556, Humayun fell from the second floor of the Sher Mandal tower while hurrying down its steep stairs to answer the call to evening prayers after stargazing at the top. He died of his injuries two days later.
Between 150,000 and 200,000 Muslim refugees sheltered at Purana Qila during the Partition of India in August-September 1947. The camp also housed over 12,000 government employees who had opted for service in Pakistan, and it remained operational until early 1948.
Yes. By December 1942, Purana Qila held 2,115 Japanese civilian internees, the vast majority transferred from Singapore. They were housed in tents offering little protection from extremes of cold or heat reaching 120 degrees, and the Japanese government formally protested the conditions.
The Qila-i-Kuhna Mosque was built by Sher Shah in 1541 as a Friday mosque for the sultan and his courtiers. Its prayer hall measures 51.20 metres by 14.90 metres and features five horseshoe-shaped pointed arches; it is regarded as a transitional example between Lodhi and Mughal architectural styles and is the best-preserved building in Purana Qila.