There was a Byzantine Dark Age in the 7th and 8th Centuries where perfume lived under the rubble of previous cities hiding from Arabic and other invaders. The Roman aqueducts went into disrepair and people went back to drinking from wells. There was a major population collapse. They did make some cool devices though like clocks and mechanical lions, as well as Greek fire. http://www.patheos.com/blogs/anxiousbench/2016/06/the-byzant...

I wasn't aware of that, thanks!

Oh, we had the Dark Ages in Italy too: roads became unsafe and eventually disappeared; there were constant wars, which resulted in people literally running for the hills, building towns in places that were easy to fortify rather than easy to reach (as it had happened in peaceful Roman times), which collapsed the economy even further; and aqueducts fell into disrepair (triggering epidemics). The population dropped, especially in locations hard to defend - Rome itself crumbled into ruins; aristocratic culture became predominantly martial, and artisanal classes shrunk dramatically because of the economic collapse. Manuscripts were burnt or locked up in monasteries, as the Church claimed exclusive rights to all cultural activity.

This only improved when the Mediterranean coastal cities managed to build up enough military strength to ensure a reasonable degree of safety over pirate-infested sea routes, "rebooting" the economic landscape. Their contacts with the now-consolidated Islamic states eventually resulted in the "rediscovery" of classical knowledge, that Islamic scholars had preserved (and built upon) in superior ways.

It's true that there was some technological progress even during the Middle Ages, but it was largely limited to immediately-practical purposes: agriculture and war.

Rome's population shrank from ~1 million to ~35 000: http://worldpopulationreview.com/world-cities/rome-populatio...

"slavery was no longer a major sociological or economic factor."

Slavery was still an important economic factor in the early middle ages ("Dark ages").

"By ...(741–752), Venice had established a thriving slave trade, buying in Italy, and selling to the Moors in Northern Africa. .. Caravans of slaves traveled from Eastern Europe, through Alpine passes in Austria, to reach Venice."

https://en.wikipedia.org/wiki/Slavery_in_medieval_Europe

The Venetians in this were just traders, slavery was a business not a part of the society. Most of the unskilled labour was done by peasants who's rights were different across Europe. From being slaves in all but name (not allowed to leave the land, and the land could be bought and sold), through having to work, but otherwise having a decent amount of freedom, to owning a small plot of land.

Venetians, and especially the Genoese had large slave populations at the time. This source quotes up to 10% of the population being slaves around 1400:

https://books.google.dk/books?id=G4dECgAAQBAJ&pg=PT28&lpg=PT...

Yeah, especially the Genoese. They dominated the Black Sea slave market all throughout the 1300s and the early 1400s, they used to buy them from the Mongols, on the Black Sea Northern shores, and ferry them (so to speak) down South to Pera (across the Golden Horn from Constantinople) where they were selling them.

Thanks! I'll take a look.