E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Ex Pede Herculem.
From this sample you can judge of the whole. Plutarch says that Pythagoras ingeniously calculated the height of Hercules by comparing the length of various stadia in Greece. A stadium was 600 feet in length, but Hercules stadium at Olympia was much longer. Now, says the philosopher, as the stadium of Olympia is longer than an ordinary stadium, so the foot of Hercules was longer than an ordinary foot; and as the foot bears a certain ratió to the height, so the height of Hercules can be easily ascertained. (Varia Scripta.)