There are a number of myths and legends associated with the origin of the name ''Delhi''. One of them is derived from ''Dhillu'' or ''Dilu'', a king who built a city at this location in 50 BCE and named it after himself. Another legend holds that the name of the city is based on the Hindi/Prakrit word  (''loose'') and that it was used by the Tomaras to refer to the city because the iron pillar of Delhi had a weak foundation and had to be moved. According to Panjab Notes and Queries, the name of the city at the time of King Prithviraj was , and that  and  are probably derived from the old Hindi word  meaning "eminence". The former director of the Archaeological Survey of India, Alexander Cunningham, mentioned that  later became . Some suggest the coins in circulation in the region under the Tomaras were called ''dehliwal''. According to the Bhavishya Purana, King Prithiviraja of Indraprastha built a new fort in the modern-day Purana Qila area for the convenience of all four castes in his kingdom. He ordered the construction of a gateway to the fort and later named the fort ''dehali''. Some historians believe that ''Dhilli'' or ''Dhillika'' is the original name for the city while others believe the name could be a corruption of the Hindustani words ''dehleez'' or ''dehali''—both terms meaning "threshold" or "gateway"—and symbolic of the city as a gateway to the Gangetic Plain.