Harry Turtledove’s Agent of Byzantium is set in an alternate world where Islam never emerged, thus the Byzantine Empire never fell and Persia remained Zoroastrian. Government agent Basil Argyros travels all over the empire on various missions (one of which involves labor relations, between the elite of Alexandria and the stonemasons who won’t work on restoring its famous Lighthouse) – and slaves and slave markets are nowhere visible, nor mentioned.
A couple of months ago at Necronomicon in Tampa I got the chance to ask Turtledove about this. Were there no slaves in the Byzantine Empire in our timeline? He replied, very few. In the “high” Roman Empire they were many, but by the time the Western Empire fell they had gradually become serfs or peasants.
The Byzantine peasantry of the eighth and ninth centuries had also become uniform. whereas Libanius in the fourth century might assert that slaves were ubiquitous, and John Chrysostom, in his treatise On Vainglory, used the term for slaves more frequently than those for God, slaves had evidently become quite rare at the time of the Farmer’s Law. Nor is there any trace of coloni.
From the introductory chapter of Change in Byzantine Culture in the Eleventh and Twelfth Centuries by A. P. Kazdhan and Ann Wharton Epstein ( 1985, University of California Press ).
Just for reference the Farmer’s Law was enacted somewhere in the 7th or 8th centuries ( the exact date in unknown ). So between the 4th and 7th centuries, slavery had slowly petered out except for household slavery for the wealthy, which of course lingered for a good long while.
Here’s a book review, one line of whichis “Constantelos’s discussion underscores the need for a thorough investigation of slavery in the Byzantine Empire and throughout the whole Mediterranean basin …” which indicates the subject really needs more study. http://links.jstor.org/sici?sici=0038-7134(199410)69%3A4<1143%3APSAPIT>2.0.CO%3B2-K
This cites claims: " The introduction of Christianity toward the end of the Roman Empire had no effect on the abolition of slavery, since the church at that time did not oppose the institution. However, a change in economic life set in and resulted in the gradual disappearance of the agricultural slaves, who became, for all practical purposes, one with the coloni (tenant farmers who were technically free but were in fact bound to the land by debts). This process helped prepare the way for an economy in which the agricultural slave became the serf.
The semifreedom of serfdom was the dominant theme in the Middle Ages, although domestic slavery (and, to some extent, other forms) did not disappear. The church began to encourage manumission, while ignoring the fact that many slaves were attached to church officials and church property. Sale into slavery continued to be an extreme punishment for serious crimes.
Slavery flourished in the Byzantine Empire, and the pirates of the Mediterranean continued their custom of enslaving the victims of their raids. Islam, like Christianity, accepted slavery, and it became a standard institution in Muslim lands, where most slaves were African in origin. In Islamic life, keeping slaves was largely a sign of wealth, with slaves used as soldiers, concubines, cooks, and entertainers and to perform a variety of other functions. Another form of Muslim slavery was in the eunuch guardians of the harems; eunuchs had been widely known in Greek, Roman, and especially Byzantine times, but it was among the Muslims and in East Asia that they were to survive longest. In Muslim countries, slavery and freedom had a much more fluid boundary than in the West, with some slaves and former slaves reaching positions of great power and prestige.
In Western Europe slavery largely disappeared by the later Middle Ages, although it still remained in such manifestations as the use of slaves on galleys. In Russia slavery persisted longer than in Western Europe, and indeed the serfs were pushed into the classification of slavery by Peter the Great. "