Which country runs the world's oldest continuous monarchy in Europe?

Denmark, whose royal line is traced to Gorm the Old in the tenth century - over a thousand years, which makes it the oldest continuous monarchy in Europe and one of the oldest anywhere. Japan's imperial line is older by tradition, though the early portion is legendary rather than documented.

The proof is a rock. The Jelling stones, raised in the 960s, carry an inscription in which Harald Bluetooth claims to have won all Denmark and Norway and made the Danes Christian - the first written use of the name Denmark within the country, on a monument still standing where it was put. The stones are sometimes called Denmark's birth certificate.

Harald also supplied the name for Bluetooth. The engineers developing a short-range wireless standard in the 1990s wanted a code name, and one of them had been reading about a king who united warring Danish and Norwegian factions - which is what the protocol was meant to do with competing communication standards. The logo is his initials in runes, bound together. Nobody expected the code name to survive to launch.