I guess this is mostly for David, but any insight welcome. I understand there has to be a default starting date, and I have a vague recollection that it advances a few years each edition, but why 1220 specifically?
Are there any interesting historical events right around the corner from game start? Some other useful property? 1+2+2+0=5 which is an auspicious year number for beginnings?
Simple curiousity, but it might give me an idea what to look for when picking start dates for my game.
Thanks
To be honest, I was wondering this myself recently. I started my campaign at 1197 (the old official start), can include Robin Hood, fall of Constantinople, and the 1st - 3rd edition source books. I havn't checked ahead, so possibly there's better stuff starting from 1220. It just seems unexpected to cut out so much cool stuff.
1220 puts them in the middle of the Albigensian Crusade, the Mongols haven't yet invaded Russia, and there's some interesting things happening in the British court.
As the others have said...and Frederick II is crowned Holy Roman Emperor (i.e. ruler of roughly Germany) in November 1220.
As opposed to ruffly Germany which doesn't show up until over four hundred years later. 
If I remember my history correctly around 1220 the Reconquista goes into high gear and the Muslim presence in Spain suffers several major setbacks shortly thereafter.
The map in the front of ArM3 says "Mythic Europe 1220". Seriously. As far as I recall that was the reason for advancing ArM4.
There are a lot of other benefits, however. In addition to the points other people have mentioned, 1220 is after Lateran IV and the foundation of the friars, which means a lot of "classic" aspects of medieval Christianity are in place.
For ArM5, I simply didn't change the date, so that ArM4 supplements would be as useful as possible.
That's kinda funny. After playing for all this time, i never noticed that the map had a different date to the rest of the book.
In our campaign which also started in 1220... we're still on our original magi 10 REAL WORLD years later. They're much older and much more powerful, but it's really worked because we're a loch legan campaign and now at the point our magi are comming into real and unassialable power, the nature of the world is turning to ash and war around them with William wallace, edward Longshanks and Berwick (our settings nearest town) being pretty much solidly under seige.
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We also began our saga in 1220, even though we began with 2nd edition - the official start year of which was 1198 (97?). I can't now remember why we chose a different year. We have been playing the same - now 3rd edition - game for twenty(ish) real world years.
How many in-game years have passed in these decade(s)-long sagas?
We have only reached Summer 1246, despite playing every week (pretty much without fail). We progress very slowly, but it seems to work.
