Many types of evidence are available that enable us to reconstruct the history and culture of ancient Mesopotamia.

Objects found in excavations can be given a rough date through their relation to other objects found above or below them in the soil. Mesopotamian sites are normally easy to identify because they are tells. These are mounds made from the accumulated levels of ruined mud-brick walls. Without proper maintenance and regular replastering, sun-dried mud brick structures need to be frequently rebuilt. Because timber is rare in Mesopotamia, any wood used for roofs, window frames and door lintels and jambs was removed for reuse, the mud-brick walls were knocked down to form a platform and a new building would be built on it. Thus, by digging down, an archaeologist will find the ruins of layer upon layer of house foundations, sometimes with small objects and broken pots still preserved, or burials beneath the floors. The deeper the archaeologist digs, the earlier should be the building, although there are complications when one building goes on being used for generations and those around it are rebuilt at different rates.

A relative chronology of the objects can be built up, depending on where they have been found in the sequence of layers of a site. Sequences from different sites can be compared. Pottery is very important as a source of evidence since it is a relatively cheap and gets thrown away when broken. Some types of pottery change their shape and decoration very quickly and sequences of pottery can be built up and compared. It is not necessary to have a whole pot to do this - think of pieces of willow pattern pottery that appear in gardens all over Britain.

Archaeologists like a violent destruction (by fire, earthquake etc), since many objects are preserved in the ruins of the building exactly where they once stood. Fire also preserves the remains of wood or textiles which would otherwise have rotted away.

Fire also bakes clay tablets and seal impressions and thus helps to preserve them. Because the Mesopotamians wrote on clay, we have over 3000 years of day-to-day records preserved: ration lists, school tablets, dictionaries, letters, literary, medical, astronomical, mathematical and historical texts, king lists etc. Some of these are copies of earlier records, but most are original texts which, in their variety and number, far exceed any other type of ancient text.

In recent years archaeologists have made use of a range of scientific techniques to help them date finds. For example:

• Radio-carbon dating (C14) is used for dating organic remains such as bone, wood and plant remains, textiles etc.. All living things absorb the Carbon 14 isotope. When they die the C14 begins to decay, by measuring how much it has decayed it is possible to work out when the plant or animal died. There is always a margin of error which means that very close dating is not possible.

• Thermolumiscence (TL) is used for the dating of baked brick and fired pottery but it is not accurate enough for close dating.

• Tree-ring dating (dendrochronology) is used for dating wood in buildings by examining the variations in the thicknesses of tree-rings caused by fluctuations in climate; these can then be fitted into an overall record of tree-rings which, with still a few breaks, goes back to around 3000 B.C.

• Ice cores. Events causing major pollution of the atmosphere, such as huge volcanic eruptions, show up as bands in ice cores drilled in places where much of the country is under permanent ice. The yearly melting and refreezing of the ice shows up as bands which can be counted, producing an absolute date for these events. If volcanic ash can then be found in archaeological levels and tied by analysis to an event in the ice cores, then these levels can be dated.