The Mongols were undefeated... for 54 years

From when Genghis Khan took power in 1206, the Mongols did not permanently lose a single battle until 1260 at the Battle of Ain Jalut (they'd lost temporarily before, only to come back and win soon after).

Note that Genghis Khan died in 1227, with an empire that was twice the size of the Roman Empire at its peak.

http://en.wikipedia.org/wiki/Battle_of_Ain_Jalut
http://en.wikipedia.org/wiki/Mongol_Empire

Best animation I've ever seen on how a key works

Demonstrates how the ridges and bumps in the key pop the tumblers into place:

http://yearinreview.tumblr.com/post/68814871127

Only with the correct amount of tension (based on the tumbler spring) will the lock open.