I visit Pottermore as much as my Live Journal... that's to say hardly... but yesterday I checked Pottermore for an update and discovered not much is happening except HP fans are fed with a list of "historicaL" Wizards till Harry Potter himself.
And there started my irritation at once.
When given in the canon the age of Hogwarts I remember some remark that Hogwarts was a thousand years old... could be in the first book already and obvious something Hermione would share with the world.*
OK so far that places the foundation of Hogwarts in about the time Edward the Confessor ruled England or at least close to the Norman Conquest... both moments are well suited, Edward favoured the feodalic system that he had encountered in the time he stayed in Normandy and that alone would be a good time to the increase of intolerance against wizardly that inspired the four wizards to found Hogwarts.
However years later when Pottermore was released there is a remark that Merlin was a Slytherin..... well is ths canon or just to be ignored.... certainly after the splendid Merlin serie of the BBC with Bradley James and Colin Morgan this doesn't sit well.
Merlin's existance is to be coined at the 6th century, traditional date for the batle at Camlann is 537.
So when the Rowling's Merlin got his education at Hogwarts, Hogwarts must have been found deep in the period the Romans ruled Britain.
I don't think any sensible wizard would be in Scotland at the time it was still called Caledonia, it was a warzone in which the emperor Septimius Severus faced a desperate guerilla war against the Caledonians and his lovely son Caracalla executed a punitive expedition in 210, which killed everyone in sight. When the founding fathers existed at that time, they likely would have played an active role on either side of the warring parties, conception of witchcraft was totally different at that time then at the close of Anglosaxon Britain.
Caledonia at time time seems to me the last place to establish a safe haven for Wizardly Education, the countryside of what would become Wales was probably better suited, but then the recluse would unlikely have an early English name as Hogwarts but bear a Celtic name like Dafadennaumochyn, which is just Welsh for Hog & Warts run through Google translator, I don't even try to image what it was called at the time Pictish was the common language in Scotland.
Also Hogwarts was founded as a castle and not a castellum of a hillfort.... the concept of castles did not appear in Brittania till William the Bastard decorated the landscape with them. This would support the idea Hogwarts was founded after the Norman Conquest in a country that was relatively stable in compassison to the great upheaval William of Normandy brought to the south.
It is of course not very important and just a pet pieve of me, but I think the editors of Pottermore should keep the canon more in line with tradition and not randomly insert unlikely facts into it.
"Merlin was a Slytherin" should be replaced with replaced with "Slytherin pretended to be a reborn Merlin"
* the canon founding date is mentioned in Chamber of Secrets by prof Binns ( page 114 bloomsbury pocket edition )
...'You all know, of course, that Hogwarts was founded over a thousand years ago - the precise date is uncertain - by the .....'