On the southern outskirts of Mehrauli is this large tank
(Hauz) said to have been built around 1230 by Shamsu'd-Din Iltutmish.
Legend Of Hauz-I-Shamsi
The tradition is that the Prophet appeared once to Iltutmish in a dream and pointed out this site to him as suitable for building the tank, which he had in mind. The next morning Iltutmish noticed here the print of one of the hoofs of the Prophet's horse, around which he built a domed platform and excavated the tank.
The famous Moorish traveller Ibn-Batua was struck by the vastness of this tank, which was supplied by rain water and in the centre of which stood a double storeyed stone pavilion, reached only by boats when full.
A red sandstone domed pavilion resting on twelve pillars located near the south-western corner of the tank, but originally believed to have been situated in its centre, is identified with the pavilion built by Iltutmish. The original stone with hoof print is believed to have been removed, the present stone being a later renewal.
The waters of the tank are regarded as sacred, and several graves of Muslim saints lie around it. The procession for the fair called 'Phulwalon-ki-Sair' or 'Sair-i-Gulfaroshan', when flower-vendors present flower-bedecked large fans at the dargah of Qutub-Sahib and at the Jogamaya temple, starts from the overflow outlet of this tank, called "Jharna".