2011 is the 60th anniversary of Emil Zatopek setting the world record for 60-minutes, twice! Zatopek ran 19,558m on 9/15/1951 and was reportedly intrigued by the idea of breaking 30-minutes for 10k twice after he noticed splits of 31:05 and 30:10 for his continuation onto 20k that same day.
So, two weeks later (September 29, 1951) Zatopek took to the track again, gunning for 20km in under 60min. He did it, running 20,052m for the hour, with splits of 29:53 and 29:58. To put this performance in perspective, at the time, only 5 men in the world besides Zatopek had gone sub-30 for 10k. Zatopek ran back-to-back sub-30s. Pretty amazing.
See Michael Sandrock, “Running with the Legends,” pp. 14-15.