The foremost cause was the immigration of artisans and merchants from the
Islamic East to India, bringing with them their crafts, techniques and
practices. Secondly, there was an abundant supply of docile trainable labour
obtained through large-scale enslavement. Finally, the Delhi Sultans
established a revenue system through which a large share of agricultural
surplus was appropriated for consumption in towns.
    Contemporary historians like Isami give us a good account of the
immigration of artisans and merchants to India. The large number of captives
obtained for enslavement in the military campaigns were trained as artisans
by their captors, and they later became free artisans by obtaining or buying
their freedom. Thus the immigration and enslavement were responsible for
the growth of urban centres and crafts, and their sustenance was provided by
the increase in the revenues with the establishment of the new land revenue
system. The ruling class, who appropriated a large part of the country’s
surplus, spent most of it in towns.
Coins of Delhi Sultanate
The gold coins which Muhammad of Ghur struck in imitation of the issues of
the Hindu kings of Kanauj, with the goddess Lakshmi on the obverse, are
without a parallel in Islamic history. For the first forty years the currency
consisted almost entirely of copper and bullion: hardly have any gold coins
been struck, and silver coins of the earlier Sultans are scarce.
    Iltutmish, however, issued several types of the silver tanka, the earliest of
which has a portrait of the king on horseback on the obverse. The latest type
bears witness to the diploma in investiture he had received from the Khalifa
of Baghdad, AI-Mustansir.
    Gold, though minted by Masud, Nasir-ud-din Mahmud, Balban and Jalal-
ud-din Khalji, was not common until Ala-ud-din Khalji had enriched his
treasury by conquests in south India. These gold coins are replicas of the
silver in weight and design. Ala-ud-din, whose silver issues are very
plentiful, changed the design by dropping the name of the caliph from the
obverse and substituting the selflaudatory titles, ‘The second Alexander, the
right hand of the Khalifate’. His successor, Mubarak, whose issues are in
some respects the finest of the whole series, employed the old Indian square
shape for some of his gold, silver   and bullion. On his coins appear the even