My medieval period was largely peaceful and went fast.
I'd had a slow start, while England had taken a huge culture lead, so I needed to do a lot more culture-building in Bjeorgvin and in total; there didn't seem to be good opportunities for conquest nearby (i.e, I would have gotten my butt kicked off the map) so I stayed peaceful.
My only ancient wonders had been the Great Wall in Nidaros (a cascade thing) and the Library in Bjeorgvin, my "monster culture" city, sorta kinda.
The first thing we did on entering the Medieval Age was declare a 5-turn party during which no work was done. Then we formed a Republic and got back to work mining more mountains around Bjeorgvin and Nidaros.
I got exactly four techs (Feudalism, Monotheism, Theology, and Education) out of the Library... those nasty AI's beelined for Education. The tech business got hairy after that; the Greeks and British were spitting out techs every couple of turns.
I ran bursty research, occasionally going hell-for-leather for unpopular techs. The first big score was Printing Press in 350 AD; that got me Engineering, Invention, Chivalry, and lots of cash. I extracted cash from leaders England and Greece, and traded for the techs from France, Russia, and the Celts, to start slowing the tech pace.
The wonder races were fierce.
England completed the Sistine in 500AD, 2 turns ahead of Bjeorgvin.
I also had a build of Copernicus well along in Nidaros. After the screaming, I switched Bjeorgvin to Copernicus, and Nidaros to Leo's.
In 510 I completed Copernicus in Bjeorgvin, and triggered a peaceful Golden Age, just in time for late-medieval wonder racing. It was helpful
England cascaded to Sun Tzu's and completed it in 520. I held my breath, terrified, waiting for the rest of the cascade, during that between-turn, but the others didn't complete.
In 530, I completed Leo's in Nidaros.
In 690, after tearing my hair out finding a way to cross-trade
for Free Artistry as my next palace prebuild neared completion,
I built Shakespeare's Theatre in Bjeorgvin. [dance]
That cheered me up. I'd mucked up the ancient build order,
so Bjeorgvin is only barely plausible as a 20k city. I needed the Bard.
Later, I had two prebuilds going, one in super-productive Nidaros, aimed at Smith's (but running Bach's until Economics showed up) and a palace in Bjeorgvin aimed at either Bach's or Magellan.
In 770, after Nidaros was on the edge of finishing Bach's and clowned up to slow it down, I gave up waiting for Economics and built J.S. Bach's Cathedral there before someone else snatched it.
In 780, the Greeks developed Economics.
OK, fine, I wriggle and wrangle and trade for economics, and switch Bjeorgvin to Smith's. Hey, a wonder is a wonder.
In 800 the Celts complete Smith's.

Oh well; at least it wasn't the British. Very painfully mortgage the Republic for Navigation (thanking the Gods my trade reputation stands), and switch Bjeorgvin to Magellan's for completion in 2.
In 810 the English complete Magellan's.
At least Greece and Russia got aced out.
In 910, I reached Theory of Gravity before anyone else except Greece. That led me into the Industrial age after I traded for Magnetism and Military Tradition, and produced enough cash to buy Steam Power from Alexander.
The AI's were squabbling in the medieval period, and Russia had begun to eviscerate France, but mostly the wars were short and inconclusive; we weren't involved in any. There weren't any dramatic resource issues that affected the Vikings.
I ended the age with no money, a comical military, very friendly relations, a good standing in technology, and a workable but sluggish culture city in Bjeorgvin, running at 38 CPT and 2700 total.
It's going to be difficult to keep all the other civs held back for the whole game, to give Bjeorgvin time to reach 20k. England has a good shot at 100k before then, because of their lightning start, and there are several looming monsters (the British, Russians, and Americans, and of course the tech-leading but smallish Greeks) who could make an interesting space race, if we let them.
So the

have their work cut out for them...
(Edit... at some point in the mid-period I finished the Forbidden Palace down in Uppsala, which is the city south of Nidaros. It made a surprisingly healthy boost to the economy, 25 GPT or so. That's why the Smith's / Magellan's wonder race was so painful; I'd already used up the FP. I suppose I could have finished the Palace in Bjeorgvin, but I wasn't sure what effect that would have had, and I had a pretty healthy core without perturbing things, so I ate the shields.)