For an archaeologist like myself, slavery is not primarily a race issue, it is to do with class, or status; take a close look at the ancient world, and a slave was merely the lowest rung on a remarkably steep social ladder.
In Mesopotamia, a the mud brick architectural heritage is less well preserved, but surviving literature provides an extraordinary insight the stories being told to explain the nature of reality. Epics like Gilamesh, Atrahasis, and Eridu are fragments of real cosmologies, to read them is to look into the past, as if viewing it in the shards of a broken mirror, reflecting things otherwise invisible to archaeology.
Their reality was an extension of a divine world, where gods presided over the [natural] forces of the world and the fates of men. A culture so dependent on nature, which is both capricious and bountiful, had gods whose actions reflected this reality. The great ancient gods could combine the extremes of human behavior with those of the natural forces they personified.
For religion to function effectively, the boundary between the heavenly and earthly worlds has to be permeable, and while in the modern world science has rolled it back, in ancient times it was still a wild frontier. The ancient Gods had sexual relationships not only with each other, but also with other living things, and in both contexts did things, which, where I live at least, would see them to be locked up for a very long time.
By the time the Sumerian epics are being written down, we also have law codes, as well as financial and administrative records, that give a detailed picture of how society worked. However, if heavenly cosmologies reflect earthly realities, in the epic and religious literature, we can catch a glimpse the belief system that drove Mesopotamian society in the late Neolithic and Bronze Age.
The Epic of Atrahasis
While most belief systems and cosmologies appear strange when viewed from outside, there is something particularly grim and unpleasant about subplot underlying the creation story in the Epic of Atrahasis.
Later in the tale, mankind has become so numerous that the chief God Enlil has his sleep disturbed by their clamour. In retribution he sends various disasters culminating in the flood. The rest of the story involves building an ark, and proceeds pretty much as expected.
Great indeed was the drudgery of the gods, the forced labor was heavy, the misery too much: the seven great Anunna-gods were burdening the [lesser] Igigi-gods with forced labour.
The Igigi-gods were digging watercourses, canals they opened, the life of the land.
The Igigi-gods dug the Tigris river and the Euphrates thereafter.
They were complaining, denouncing, muttering down in the ditch:
"Let us face up to our foreman the prefect, he must take off our heavy burden upon us! Enlil, counsellor of the gods, the warrior, come, let us remove him from his dwelling;…”
"Will you be the birth goddess, creatress of mankind?
Create a human being, that he bear the yoke, let him bear the yoke, the task of Enlil, let man assume the drudgery of the god."
Enki made ready to speak, and said to the great gods:
"On the first, seventh, and fifteenth days of the month,
let me establish a purification, a bath.
Let one god be slaughtered, then let the gods be cleansed by immerson.
Let Nintu mix clay with his flesh and blood.
Let that same god and man be thoroughly mixed in the clay.
Let us hear the drum for the rest of the time.
From the flesh of the god let a spirit remain, let it make the living know its sign,
lest he be allowed to be forgotten, let the spirit remain."
The great Anunna-gods, who administer destinies,
answered "yes!" in the assembly.
They slaughtered Aw-ilu, who had the inspiration, in their assembly.
Nintu mixed clay with his flesh and blood.
That same god and man were thoroughly mixed in the clay.
For the rest of the time they would hear the drum.
From the flesh of the god the spirit remained.
It would make the living know its sign.
Lest he be allowed to be forgotten, the spirit remained.
After she had mixed the clay, she summoned the Anunna, the great gods.
The Igigi, the great gods, spat upon the clay.
Mami made ready to speak, and said to the great gods:
"You ordered me the task and I have completed it!
You have slaughtered the god, along with his inspiration.
I have done away with your heavy forced labor,
I have imposed your drudgery on man.
Release from bondage.
In a world where gods and men interact, the stories of this relationship grow and change to reflect and explain the changing nature of mans’ experience. Two thousand years later, and European cosmologies concerning mankind’s creation and early history were dominated by the biblical accounts.
Slavery in prehistory
In the literature of the ancient world and in most early historical periods, slavery is endemic, and just the bottom of the social pile. While in European prehistory, with no written records, slavery is hard to prove, like religion, it is difficult to imagine a world without it.
Celtic slavery and bling
On the decorated Late Iron Age cauldron found at Gundestrup in Denmark, torcs are worn by most of the principle figures, presumed to be both male and female deities or mythical characters. If Gods could serve other Gods, then this does not necessarily detract from this idea that torcs symbolised some relationship of servitude with the divine.
This snapshot of feudalism shows, that in terms of tenants, around 10% of the population were ‘slaves’, compared with 14% who were ‘freemen’; the rest of the rural population, [nativi], villeins and cottars [bordars], were born into a status of servitude somewhere in between the two. [left, 11]
Feudalism in Europe is thought of as medieval, certainly this is when it is first described historically, however, Caesars description of the Celtic society in Gaul sounds very much like feudalism, and from the Early Bronze Age onwards there clear evidence of a hierarchical society.
The idea of servitude and slavery is important in Mesopotamian cosmologies, and seems to underlie most classical and early historical societies, and it is possible to view idea that ownership of land included the people who worked it, as a fundamental element in the agricultural revolution that gave rise to civilisation.
Quite when the quest for personal autonomy began as significant theme in history, is also difficult to recognize, but it was undoubtedly aided by a Judeo-Christian cosmology that no longer saw mankind as being created as slaves of the gods.
Sources & further reading http://www.museumwales.ac.uk/en/2369/ [Accessed 13/04/11]
http://www.britishmuseum.org/explore/highlights/highlight_objects/me/c/cuneiform_the_atrahasis_epic.aspx [Accessed 13/04/11]
 http://www.livius.org/as-at/atrahasis/atrahasis.html [Accessed 13/04/11]
Before the Muses An Anthology of Akkadian Literature Third Edition Translated by Benjamin R. Foster ISBN: 9781883053765 CDL Press, 2005,
 Evans, J 1872, The ancient stone implements, weapons, and ornaments, of Great Britain Longmans, London.
http://www.archive.org/details/stoneimplementsw00evaniala [Accessed 13/04/11]
 http://upload.wikimedia.org/wikipedia/commons/5/5a/Franks_casket_03.jpg [Accessed 13/04/11]
 Translated by W. A. McDevitte and W. S. Bohn
http://classics.mit.edu/Caesar/gallic.6.6.html [Accessed 13/04/11]
 http://en.wikipedia.org/wiki/File:Newark_torc.jpg [Accessed 13/04/11]
 http://en.wikipedia.org/wiki/File:StervendeGalaathoofd.jpg [Accessed 13/04/11]
 Gundestrup, Himmerland, Jutland, Denmark. The Gundestrup cauldron is housed at the National Museum of Denmark.
http://en.wikipedia.org/wiki/File:Detail_of_antlered_figure_on_the_Gundestrup_Cauldron.jpg [Accessed 13/04/11]
 Falkus, Malcolm E.; Gillingham, John, 1981, Historical Atlas of Britain
(ISBN: 0862722950 / 0-86272-295-0 ) p176
Also; Sommerville J P, Medieval English Society
http://history.wisc.edu/sommerville/123/123%2013%20Society.htm [Accessed 13/04/11]
Illustration of the Pyramid of Djoser :http://en.wikipedia.org/wiki/File:Saqqara_stepped_pyramid.jpg [Accessed 13/04/11]