Usually the centre of each seal is occupied by a realistic depiction of an animal, with above it a short line of formal symbols.

As writing develops, a standardized method of doing it begins to emerge.

This is essential to the very purpose of writing, making it capable of carrying a message over unlimited distances of space or time.

Characters are formed from the wedge-shaped marks which the reed makes when pressed into the damp clay, so the style of writing becomes known as cuneiform (from the Latin cuneus, meaning wedge).

The second civilization to develop writing, shortly after the Sumerians, is Egypt.

Its constituent parts are still the same Egyptian hieroglyphs, established more than 2000 years previously, but they are now so elided that the result looks like an entirely new script.

Known as demotic ('for the people'), it is harder to read than the earlier written versions of Egyptian.

When allowed to bake hard in the sun, the clay tablet becomes a permanent document. Significantly the chief official of many Sumerian temples is known by a word, sangu, which seems to mean 'accountant'.

But however non-literary the purpose, these practical jottings in Sumer are the first steps in writing.

The combined character, roof and bank, would then stand for a financial institution - the type of 'house' which is a 'bank'.

In about 3200 BC temple officials in Sumer develop a reliable and lasting method of keeping track of the animals and other goods which are the temple's wealth.

The Egyptian characters are much more directly pictorial in kind than the Sumerian, but the system of suggesting objects and concepts is similar.