The first cities under fire
According to Clemens Reichel, an archaeologist at the Oriental Institute, the entire area dug up during 2005 excavations at the ancient city of Tell Hamoukar was “a war zone.” About half a square mile (~15 hectares) in size, the city’s ten-foot (3 meter) high circular mud brick wall was not tall enough for defense, nor do I see evidence of projecting towers. Like the walls of biblical Jericho, then, the walls of Tell Hamoukar appear to me as flood protection rather than fortification. (Caveat: I am not an expert on ancient flood technology.) If I am right, the city leaders considered these walls good enough to defend the city from attack as well as floods, making no effort to improve them as defenses. It mattered.
Around 3,500 BC, an army from Uruk defeated these walls, demolishing and burning a large section. They left behind evidence of a concerted storming attack. Archaeologists found more than 1,200 walnut-sized, teardrop-shaped clay sling bullets (see photo) and at least 120 clay sling bullets the size of baseballs during the dig. Although there is a suggestion that this bombardment reduced the wall, this seems dubious to me. I think it is far more likely that sappers did that work under the supporting fire of the bombardment. This would have followed the assault force, which would have used ladders in “escalade.”
Although some of the clay pellets were a bit fresh, deforming on impact, they would still have struck someone with quite a lot of force. By keeping the wall clear of defenders this way, the army of Uruk made operations against the wall itself possible. It is very common in ancient siege for armies to take their time filling in moats, building up ramps, etc, in preparation for an attack on a section of wall, and this is far easier to do without the defenders daring to expose themselves in order to shoot arrows or stones at you while you are busy. Indeed, the walls may have only been slighted after the city surrendered, as this is a common measure used to discourage future rebellion by subjugated towns.
Although it is impossible to perfectly reconstruct the sequence of events that led to this conflict, or what exactly took place here, the dig team concluded that Uruk occupied the city afterwards. Thus we are left with the picture of an imperial power, a city-state at the dawn of civilization, marching (and probably sailing) thousands of troops hundreds of miles up the Tigris river, equipping and supplying and training them to attack city defenses, and successfully carrying out that extended campaign. Getting an army to a battle is impressive all on its own; camping that army outside of a city, and then attacking it successfully after a period of preparation, is a much harder military development than raising the army, or getting it to a fight with another army.
To make a rather long analysis short, the material, logistical, and even moral costs of siege are higher than that of field battles. Troops do not like to occupy the same place for very long, and it is in fact very dangerous for the besieging army in an age before proper field sanitation. Nor are most troops eager for high-risk missions such as storming defenses. To sack a city with walls, even bad ones like Tell Hamoukar, requires such administration, organization, preparation, and most of all systems of reward, that only states really have the resources to achieve it.
Just as walls are intimately related to state formation, so is the art of poliorcetics, defending and defeating those walls. It is an arms race at least as old as civilization.