Uruk 3500-3000 B.C.E.

Uruk
It all begins at the city state of Uruk and the period which bears its name (also known as Old Babylonian).  Uruk eventually dominated all of southern Mesopotamia and it was at Uruk that the system of Mesopotamian irrigation and administration was perfected. The city state was made up of the city itself and the environs, which was largely dedicated to agriculture.

A Theocracy
Within the city there was a large temple complex dedicated to the patron goddess of the city, Innana, and all agricultural produce of the environs of the city would be “given” to her and held at her temple. This food, sometimes after processing (grain into flour, barley into beer) would then be given back to the citizens of Uruk in equal share at regular intervals. The head of the temple administration, the chief priest of Innana, would serve as the political leader. The first great theocracy.

Cuneiform
We know the details of this theocratic administration so well because of the use of writing, in cuneiform script, and the many documents which remain. 

Cylinder Seals
These documents, tablets made of dried mud, were sealed in clay envelopes and signed using cylinder seals, small pierced spherical objects, like long beads, which were carved, in reverse (called intaglio), with a unique image and sometimes the name of the owner.

The seal would be used to roll over the soft clay of a tablet to function as a signature (see below). The minute images on these seals use a system of iconography which identifies the associations and rank of the owner.  

Jasper cylinder seal and impression showing monstrous lions and lion-headed eagles,
Mesopotamia, Uruk period, 4100 BC–3000 BC, (Musée du Louvre, Paris)

Images sources:
Map
Clay tablet from Alalakh still in clay envelope. Dated 1720 BC.
Jasper cylinder seal and impression: monstrous lions and lion-headed eagles, Mesopotamia, Uruk Period, 4100 BC–3000 BC, (Louvre)