Interesting piece of gaming history. In the Blackmoor campaign (i.e. Dave Arneson's campaign) the first dungeon crawl had only one survivor. This was his first adventure and for surviving it he was promoted to "hero"-level, basically the equivalent of 4th level. No xp involved at that point. I'm not sure when the concept of xp was created.
They only had three levels though right? Normal, Hero (4HD) and Superhero (8HD)?