Delhi is northern India's largest city. One part of it, known as New Delhi is officially designated the capital of India, but the names are often used interchangeably. Delhi is said to be one of the oldest existing cities in the world, along with Damascus and Varanasi. Legend estimates it to be over 5,000 years old. Over the millennia, Delhi is said to have been built and destroyed 11 times. The oldest alleged incarnation of the city shows up in the Indian mythological epic Mahabharata as Indraprastha. The earliest historically recognized version of the city is Qila Rai Pithora ??? This dates back to the 10th century A.D. as per available historical records. Also known as Rai Pithora, this city was the capital during the reign of Prithviraj Chauhan, the local hero famous for his first defeating, before finally losing to, the marauding invaders from central Asia (Muhammad Ghori in particular). Chauhan's ancestors are said to have captured the city from the Tomar Rajputs who were credited with founding Delhi. Anangpal, a Tomar ruler possibly created the first known regular fort here called 'Lal Kot', which was taken over by Prithviraj and the city extended. Some of the ruins of the fort ramparts are still visible around Qutab Minar and Mehrauli. Mehrauli ??? Muhammad Ghori managed to defeat Prithviraj Chauhan in battle in 1192. Ghori left his slave Qutub-ud-din Aibak as his viceroy, who in turn captured Delhi the subsequent year. After Ghori's death in 1206, Aibak proclaimed himself the ruler of Delhi and founded the slave dynasty. Qutb-ud-din contributed significantly in terms of architecture by getting Mehrauli built. His most prominent contribution is the starting of Qutab Minar. This 72.5 m tall tower was built across three generations and finally completed in 1220AD. A visitor to the Qutab Minar could also see the mausoleum of Kaki, Shamsi Talao and some other mosques. The Slave dynasty ruled until 1290, among them was Razia Sultan who ruled for just three years, but became a historic figure for being the first empress in India. Siri - Qutuddin Aibaq's 'Slave Dynasty' was followed by the line of Khilji (or Khalji) rulers. The most prominent among the six rulers was Allauddin who extended the kingdom to the south of Narmada and also established the city of 'Siri'. Among some of the remaining ruins, is part of the Siri Fort in the greater Hauz Khas area. The madrasa at Hauz Khas was constructed during Allauddin's reign and bears the stamp of West Asian architecture. Hauz Khas is more often visited today for the chic botiques and restaurants. Tughlakabad - Exactly as it happens during the fall of a lineage of kings, after the Khilji's there was administrative chaos for sometime as the last Khilji ruler was slain by Nasruddin Mohammed. Ghiyasuddin Tughlaq (a Turk governor) invaded Delhi in the 1320s, started the Tughlaq dynasty, and founded the city of Tughlakabad. The ruins of the large fort still remain. His descendent Muhammad Bin Tughlaq raised the fort walls, created another city called Jahapanah (which enclosed the area between Siri and Qila Rai Pithora). Tughlakabad continued, however, to be the main capital city. Muhammad Bin Tughlaq is also known as the mad king for wanting to move the capital from Delhi to Daulatabad (now near Aurangabad in Maharashtra) and making the entire population travel, only to return in a few years because of water shortage in the new town.