10% is easy with modern equipment and yeast, but remember that pure yeast strains didn't exist until Emil Hansen isolated one at the Carlsberg Laboratory in 1883 [1]. In Early Modern times people used whatever yeast happened to grow locally, saved between batches as "barm" (flocculated yeast). Selection pressure with this propagation technique is primarily for flocculation ability, and it produces strains much more flocculant than wild strains. These strains have lower attenuation because they drop out of suspension before all the sugar is fermented. Try reaching 10% ABV with a traditional English strain like Fermentis Safale S-04 - it's pretty much impossible.
Despite what Fermentis claims, I don't think S-04 is that "traditional." It's a beast of a yeast and it will keep going and going. 10% is pushing the upper end of its range, but more because of the limited alcohol tolerance of the yeast than because of anything else.
It makes sense if you consider where it came from-- it was supposedly used in the tower fermenters of the old Whitbread brewery. Where the most important thing was a cockaroach-like ability to survive and keep fermenting no matter what, as new wort was fed into one end of the system and fermented beer came out the other end.
I don't like s-04 because it throws lactic acid, which tastes like someone squeezed a lemon into the beer. Not what I want in an English ale.
If you want traditional, go with something like Danstar Winsor. But be warned, the yeast can't ferment maltotriose, and it struggles with gravities above 1.040.
As to what early moderns did-- well, they could have just put sugar in the wort if they wanted to push up the ABV. I guess that wouldn't apply back in the middle ages though (not sure what you are considering early modern).
I was told by a biologist that old houses were full of airborne yeast (saccarome cervisirae) which origins where the «Chaumes» roof. [confirmed by a link in the paperspace]
[1] https://en.wikipedia.org/wiki/Emil_Christian_Hansen