Urbanisation is the process by which small villages grow into larger ones, then to towns, then to cities and eventually large urban city centres. Urbanisation began in ancient Mesopotamia in the Uruk Period (4300-3100 BCE) for reasons scholars have not yet agreed on, though there are many assumptions. Of course, at a very basic level, urbanisation does imply the concentration of a large population, but an urban centre is not just an over-grown village. Urbanisation in it's true form means the concentration in a particular settlement, of a fairly large population, pursuing diverse economic activities and having a high degree of interdependence. one of the main features of urbanisation is extensive specialisation and division of labour provided with lack of self sufficiency. Cities have a complex and social economic system. There are structures of authority for managing disputes. Moreover, cities have specific buildings for a specific function for maintaining order.
According to Gordon Childe, there were several reasons for urbanisation at this time.
Centralised accumulation of capital resulting from the imposition of tribute or taxation.
The invention of writing
Advancement towards sciences
Emergence of class stratified society
Long distance trade
The freeing of a part of the population from subsistence tasks for full time craft specialisation.
were some of the reasons which resulted in urbanisation. Thus, "Urban Revolution" was the name given to it by Gordon Childe.
Production of metal possess the presence of some specialists. Society should be able to support these specialists by food and shelter so that they can do their work rather than depending on subsistence only. The use of metal can only become widespread when a group of specialists permanently withdraw from agriculture or food production. No doubt that all this happened in Mesopotamia.
Another problem with southern Mesopotamia is that they do not possess any deposits of copper. The metal had to be imported from Iran and Anatolia. This trade had to be carried out by exchanging the surplus produce of Sumeria for raw materials that the region lacked. So it was very important to have a regular mechanism to regulate the production and redistribution of the surplus. This indeed increased the demand for the surplus which was obviously not met by the farmers initially. This increased the need for a compulsion to be imposed on the farmers to produce surplus on a permanent basis.
Therefore, Systematic extraction of the surplus created conditions for its redistribution in an inequitable manner. Some groups in the society were able to take control over a disproportionately large share of the surplus ( Chieftains, priests, warriors ). On the other hand there were groups which were denied their legitimate share of the surplus ( Peasants, artisans, slaves ). This marked the division of the society into classes: a class of people who actually produced and a class of people which took over the bulk of surplus and possessed political and economic power.
State formation
In ancient Mesopotamia, the state was primarily an instrument to perpetuate the domination of class which appropriated a disproportionately large share of the surplus. The state performed other functions as well, such as keeping conflicts in check, providing protection, promoting trade and organising irrigation. The pattern of state formation in Sumeria which we found, where the temples occupied a prominent place, should not be regarded as a universal pattern of state formation.
State formation was not an isolated event but was closely related to metallurgy, surplus production, specialisation and class differentiation all of these which when added together with writing gives birth to urbanisation. Urbanisation; surplus production; complex social systems; division of labour; existence of a state; organised religion; use of metal; development of writing are some of the traits of civilisation.