The idea of the sleeping, or just waiting, hero seems to be not-rare in European folklore. It can be found a few other places as well. The pattern is that a great figure from the nation’s past, either real or the time before written history, did not really die, but sleeps in a mountain, or on a hidden hill or island, or in a gateway or secret wall. In time of greatest need, the person will awaken and return to save his people from danger. Often it is a monarch, like Frederick I Barbarossa, Charlemagne, King Arthur, Constantine XI of Constantinople, Gengis Khan or others. Sometimes it is a warlord, like Francis Drake (who can be summoned), Field Marshall Alexander Suvarov, Holger Dansk, Vlad III, or the knights of Alderly Edge in England.
The archetype can be found other places, although sometimes it is the bad guy who is sleeping and should not be awakened. In a few cases, one wonders if folklore gatherers tucked a different legend into the pattern, or the idea was picked up from Europeans (such as Tecumseh of the Shawnee returning from hiding/sleep). Related to this is the idea of the Seven Sleepers of Ephesus*, originally a Christian story saying that seven (or eight) believers hid in a cave during the persecutions of Diocletian, and they remained asleep and hidden for two hundred years or so, until a Byzantine emperor had the cave opened and the seven (or eight) woke up and testified to the Lord’s power. Islam has a version of the story as well in Sura 18.
The archetype is very common in northern Europe and the British Isles, and can be tracked to Celtic tales. It appears in Plutarch, who quotes an earlier Roman story collector who picked up a version of the “sleeping hero” story around AD 80-100 or so.
In some versions of the story, an external sign will call the hero/king to arise and save his people. In England, beating Drake’s Drum was said to do it, and popular legend has that during the Battle of Britain, people heard a booming sound, like a hidden drum being struck. Frederick Barbarossa will awaken when the ravens leave the Kyfferhauser Mountain in the Harz.** Holger Dansk and Arthur sleep until needed. Anyone who tries to rob the sleeper, or awaken him prematurely, faces doom.
Academics have lots of theories about the stories, and the rise of nationalism in the 1800s and the desire for a hero who’s not really dead, but waiting for the hour to come. I suspect some of the stories “were discovered” during the 1800s, or were modified to fit the pattern better. Others track a long way back, and probably include older elements that are native to the associated places. Barbarossa in the Harz Mountains might well be one of those, ditto Arthur. In Arthur’s case, Wales has several pre- and post-Arthurian hidden heroes or kings, so he fit into that portion of the Matter of Britain quite well. Holger Dansk***, or Ogier the Dane, comes from the Matter of France – the stories of Charlemagne and his paladins – and appears in several of those stories, then shifts to Danish lore. He doesn’t appear in Scandinavia until after 1200 or so, so how native he is is up for debate. Except in Denmark, where he’s been adopted with enthusiasm.
People want heroes, and symbols. The sleeping king serves very well, and goes back a very long way. It’s inspiring at times, comforting at others, to think that a great man will arise to save/protect his people in their darkest hour. Some groups adopted the name of the sleeper, like the Danish Resistance on WWII. Alas, Barbarossa got a less inspiring association from that conflict. Which makes you wonder what it would take to awaken him. I don’t care to be on the European mainland should that happen, thank you.
*There’s a small church in Austria, on the old Roman road along the Danube, that is dedicated to the Seven Sleepers. It’s the only one I’ve ever encountered with that dedication.
**Given all the uncanny stuff associated with the Harz, this one doesn’t surprise me at all.
***I spotted a fellow grad student with a Holger Dansk tee-shirt from a certain counter-jihad blog. We got along very well after comparing screen names and bona fides.
Cat Rotator's Quarterly 
Stephen Vincent Benet gave us an American version in “The Devil and Daniel Webster”:
‘Yes, Dan’l Webster’s dead—or, at least, they buried him. But every time there’s a thunder storm around Marshfield, they say you can hear his rolling voice in the hollows of the sky. And they say that if you go to his grave and speak loud and clear, “Dan’l Webster—Dan’l Webster!” the ground ‘ll begin to shiver and the trees begin to shake. And after a while you’ll hear a deep voice saying, “Neighbour, how stands the Union?” Then you better answer the Union stands as she stood, rock-bottomed and copper sheathed, one and indivisible, or he’s liable to rear right out of the ground. At least, that’s what I was told when I was a youngster.’
I would be entertaining, to say the least, if Daniel Webster r’ared right out of the ground in the present-day Northeast.
It would serve a lot of people I knew there right….
Gotta admit, could be hilarious if Andrew Jackson, Patton, Lieutenant Furlong, etc., showed back up and started causing trouble.
Horrifying also, perhaps.
But, it is not like we could not also do a lot of those things, if it mattered enough for us to really want to.
I’m pretty sure the EU’s first project was to find these locations, and entomb them in concrete.