death to capslock

Occasionally, something on Pottermore actually makes sense and supplements what's in the books rather than breaking all of time and space. Here's one that I think works: Ignatia Wildsmith (1227-1320) invented Floo Powder some time in the 13th century.

What other things happened around this time?

• The Golden Snidget was used in Quidditch for the first time in 1269 and quickly became an integral part of the game;
  
• The first Triwizard Tournament was played around 1294;
  
• The Black family allegedly started marrying only other magical people.

Let's say Ignatia invented Floo Powder around 1260 and started marketing it pretty quickly. Within a few years, Quidditch development goes from introducing and refining new elements over the course of a couple of centuries to the latest addition becoming so popular so quickly that the Snidget is an endangered species within decades. After about 35 years, they organize a major international sports tournament with wizards on the Continent and probably Scandinavia.

This is about what you'd expect if travel suddenly became easier and faster. Anyone--not just those who can Apparate, but sick people, children, magically weak people, groups of people too large to side-along all at once, etc.--can suddenly instantly transport themselves at least anywhere in Britain. (We don't know the limits of Floo travel, but the kids Floo from either London or Ottery-St.-Catchpole, I can't remember which, to Hogwarts at one point. So it's at least that far.) And suddenly, they can chat with each other in real time instead of having to wait for an owl to arrive with a letter. We know how much cars, airplanes, and telephones have changed our own societies; imagine if we had (smoky, awkward versions of) FaceTime and Star Trek transporters seven hundred years ago.

This also makes a plausible turning point toward wizards separating from Muggle society. They went to magic school before, and had a national (or possibly international, depending on how much of the British Isles the Wizards' Council covered) magical advisory council. But they still lived in Muggle communities for the most part, and were limited in how much they could visit and communicate with other magical people once they'd graduated. So they had lots of reasons to integrate into Muggle society, marry Muggles, etc., even if they did also have their far-flung alumni/hobby community with a few traditions of its own. But once it became easy even for (temporary or permanent) non-Apparaters to visit their children even if they'd married people hundreds of miles away, well, that opens up some possibilities. Now marrying your school sweetheart doesn't mean losing your family support system--Mum can still help watch the baby even if she lives in Devon and you live in Yorkshire. A family of wizarding apothecaries can make a marriage alliance with another such family instead of whoever is available locally. And if you didn't meet someone at school, now you have more opportunities to meet someone at one of those increasingly well-attended sports games instead.

I doubt that the Blacks really have no Muggle or Muggle-born marriage partners going that far back, but I can believe that they started strongly preferring magical spouses and seeing themselves as set apart from their Muggle neighbors around that time.

And after a couple of centuries of the magical community growing increasingly defined and separate, you get witch hunts...

It probably isn't perfect, but this bit of backstory works well enough that I wonder if it happened by accident, or if someone other than Rowling made up the date.