Qutub Minar, at 74 meters, is the second tallest minar in India after Fateh Burj at Mohali. Qutub Minar, along with the ancient and medieval monuments surrounding it, form the Qutb Complex, which is a UNESCO World Heritage Site. Made of red sandstone and marble, Qutub Minar is a 73 meter tall tapering tower with a diameter measuring 14.32 meters at the base and 2.75 meters at the peak.Inside the tower, a circular staircase with 379 steps leads to the top. In 1200 CE, Qutub-ud-Din Aibak, the founder of the Delhi Sultanate started construction of the Qutub Minar. In 1220, Aibak's successor and son-in-law Shams-ud-din Iltutmish added three storeys to the tower. In 1369, lightning struck the top storey, destroying it completely and Firoz Shah Tughlaq carried out restoration work replacing the damaged storey with two new storeys, made of red sandstone and white marble. Qutub Minar is surrounded by several historically significant monuments, which are historically connected with the tower and are part of the Qutb Complex. These include the Iron Pillar of Delhi, Quwwat-ul-Islam Mosque, Alai Darwaza, the Tomb of Iltutmish, Alai Minar, Ala-ud-din's Madrasa and Tomb, and the Tomb of Imam Zamin. Other minor monuments include Major Smith's Cupola and Sanderson's Sundial.