At the foot of Mount Olympus bubbles up a spring that changes its flavour hour by hour, night and day, and the spring is scarcely three days’ journey from Paradise, out of which Adam was driven. If anyone has tasted thrice of the fountain, from that day he will feel no fatigue, but will, as long as he lives, be as a man of thirty years.

—From the wonderful letter of Presbyter Johannes sent to various Christian princes in 1165