After loading up a
lot of 600AD starts as Russia, I finally got one which flipped a German city (Essen) on my Russian spawn. Conveniently, the declaration of war also doubles the starting army for Russia. With the extra units, I was able to subjugate Germany to vassal status from the outset as well as capture a whole bunch of workers to start improving terrain around my empire.
Next targets were Constantinople, Athens and Rome. A couple of suicide catapults and the veteran Horse Archers finished the job. At the same time, Vikings had not expanded towards the east so I managed to settle Lulea (I think the best city-site in Scandinavia).
An early trireme was whipped from Essen and sailed immediately to make contact with Mali. Trading for Divine Right quite early meant I was able to build Spiral Minaret before Arabia, which was very important. I think I locked in 100% science from that point and never adjusted the research setting for the remainder of the game.
Netherlands vassalised voluntarily just as I circumnavigated the world, so I gifted them a few techs to get them along to Astronomy and made sure that they were the first European colonial power to settle the new world. Aztecs and Incas were subjugated by force. Germany finally collapsed at about this point, but my Dutch vassal picked up most of the pieces.
After the Turkish spawn, their culture impeded Constantinople too much so I razed Sogut and forced their capitulation. My last vassal was China, who volunteered shortly after the Mongols collapsed and then all the independent troops headed for Beijing. China became an awesome vassal, supplying all the missing resources that Russia doesn't normally get access to.
Over the last 300 years, there wasn't much to do other than avoid accidental victories other than historical. My focus was so much on avoiding a domination win that I nearly won a cultural victory by mistake right at the end. Constantinople was about to become my third legendary city and trigger cultural victory in just one more turn.