From the ArcaMax Publishing, Jokes Newsletter:
http://www.arcamax.com/news/jokes/s-365746-170052
A bus load of tourists arrives at Runnymede. They gather around the
guide who says, "This is the spot where the barons forced King John to
sign the Magna Carta."
A fellow at the front of the crowd asks, "When did that happen?"
"1215," answers the guide.
The man looks at his watch and says, "Darn! Just missed it by a half
hour!"