India"s historic national capital Delhi is known as the "City of Seven Castles" where "Castles" represent forts that have been built through the chronicles, with massive formidable and impregnable walls that have witnessed numerous battles and survived the test of time.

Red Fort, Delhi
The UNESCO World Heritage Site Red Fort is a prime historical monument of India, a majestic fortress that most notably served as the capital of the Mughal Empire and the residence of Mughal Emperors for nearly 200 years till 1857. It was constructed in red sandstone when Emperor Shah Jahan decided to shift the capital of the empire from Agra to Delhi, establishing a new city called Shahjahanabad, present day Old Delhi. After the ouster of Bahadur Shah Zafar, the last Mughal Emperor in India, the Red Fort was taken over by the British in 1857 who controlled it as a military cantonment. Post independence, it witnessed a few changes to its construction and continued to be a military cantonment, with a significant portion under the control of the Indian Army. In December 2003, it was handed over to the Archaeological Survey of India (ASI) for restoration.

Salimgarh Fort, Delhi
Salimgarh Fort is another historical fort in Delhi that witnessed the Mughal regime and the British Raj. It was erected in 1546 AD by Salim Shah Suri, son of Sher Shah Suri. In 1540 AD when Sher Shah Suri defeated Mughal Emperor Humayun and ousted him from Delhi, the Sur dynasty was established lasting till 1555 AD when Humayun recaptured his kingdom. During the Mughal reign in later years, while establishing the Red Fort and Shahjahanabad, several Mughal rulers including Emperor Shah Jahan had camped at this fort. It is also believed that Humayun himself had camped at the fort for 3 days before initiating his attack to recapture Delhi.

Purana Qila, Delhi
Purana Qila is one the oldest forts in Delhi, built by Sher Shah Suri. Excavations by the ASI at Purana Qila have unearthed painted grey ware dating 1000 BC, and with a continuous cultural sequence from Mauryan to Mughal through Shunga, Kushana, Gupta, Rajput and Sultanate eras, confirming the site"s antiquity.

Qila Rai Pithora, Delhi
Qila Rai Pithora was a 12th century fortified city established by Prithviraj Chauhan, when Chauhan Rajputs had taken over Delhi from Tomar Rajputs. The fort, remains of which are visible across South Delhi, was the capital of Tomars, Chauhans and the Slave Dynasty during their rule over Delhi through the 12th and 13th centuries.

Tughlaqabad Fort, Delhi
Tughlaqabad Fort is a ruined fortress in Delhi stretching over 6 kilometres. It was constructed by Ghiyas-ud-din Tughlaq, the founder of Tughlaq dynasty of the Delhi Sultanate of India in 1321.