Delhi. Dehliwala, the standard coin, was a silver-copper alloy with a uniform weight of 3.38 grams, of which 0.59 grams was Silver. The major source of silver for the Delhi mint were coin hoards from Central Asia. Another source was European silver which made its way to Delhi via the Red Sea, Persian Gulf through the ports of Gujarat. By the 1220s, supply from Central Asia had dried up and Gujarat was under control of hostile forces. In response to the lack of silver, Iltutmish introduced a new bimetallic coinage system to Northern India consisting of an 11 grams silver tanka and the billon jital, with 0.25 grams of silver. The Dehliwala was devalued to be on par with the jital. This meant that a Dehliwala with 0.59 grams of silver was now equivalent to a coin with 0.25 grams of silver. Each Dehliwala paid as tax, therefore produced an excess 0.34 grams of silver which could be used to produce tankas. The new system served as the basis for coinage for much of the Sultanate period and even beyond, though periodic shortages of silver caused further debasement. The tanka is a forerunner to the Rupee. Islamic culture During Iltutmish's reign, the city of Delhi emerged as the centre of Islamic power and culture in India. He patronized several scholars, including historian Minhaj-i-Siraj and the Sufi mystic Qutbuddin Bakhtiar Kaki. Minhaj states that Iltutmish's patronage attracted several scholars and other prominent people to Delhi, especially from Persia, which had fallen to the Mongols. Iltutmish's court is reported to have had raised seats for distinguished scholars and saints, as opposed to lower seats for others. This is suggested by Fawa'id-ul-Fu'ad, a near-contemporary work, which describes a quarrel between Shaikh Nizamuddin Abul Muwayyid and Sayyid Nuruddin Mubarak Ghaznavi over choice of seats in Iltutmish's presence. Fawa'id-ul-Fu'ad mentions an anecdote about Iltutmish's patronage to scholars: Nasiri, a poet in need of a royal award, composed a qasida in praise of Iltutmish. However, while he was in the middle of reciting the poem, Iltutmish left the recital to attend an urgent administrative matter. A dismayed Nasiri thought Iltutmish would forget him, and lost all hope of getting the royal award. But as soon as Iltutmish was free, he came to Nasiri, recited the first line of the qasida from his memory, and asked Nasiri to complete his recital. Architecture Iltutmish invested in numerous waterworks,