of the iron mines of south Bihar and local
  that initially the technology was in the hands of itinerant smith. The routes
  of the itinerant smiths may have built up a circuit of trade connecting local
  levels of production.
Nature and Course of Urbanisation The origin of some of the nigamas
may also be traced to villages specialising in particular craftsmen such as
potters, carpenters and salt makers, which may have become small
specialized markets and later more general market centres. A corroboration of
the nigama as a market town is available from numismatic evidence where a
series of early coins carry the legend ‘negama’ suggesting that they were
issued by a nigama. In the context of very large cities the word has also been
interpreted as the ward or section of a city where professionals working in a
particular craft would live and work, again indicating some commercial
connections.
    The existence of nigama may also have provided a base to some rising
towns. A distinction has to be made between the city as a political centre and
one which combined both political and commercial functions. There is a
difference in the ethos of towns which were primarily political centres such
as Hastinapur,
    Indraprastha, Ahicchatra and Ayodhya and those which combine political
with commercial functions, such as Saravasti, Kausambi, Vaisali and
Rajagrha.
    The growth of urban centres may also have been quicker in the middle
Ganga valley since the nuclei of the gana-sanghas were the settlements
occupied by members of the raja-kula. As they lived in nucleated groups
rather than on their own lands, there was greater potential for the transition of
such settlements into towns.
    The term pura was often employed for towns and originally meant a
fortified settlement or a locality. Fortifications were associated with political
centres which were either the residence of the raja and his entourage or of the
families of the raja-kulas in the gana-sangha system. The fortification
enclosed the urban settlement and separated it from the surrounding areas,
thus demarcating the urban from the rural. But this separation was by no
means absolute since the links between the two remained strong.
    Nagara was the common