CYLLENE, in Ancient Geography, a mountain of the Peloponnesus, in the N.W. corner of Arcadia, and close to the confines of Argolis and Achaia. It is frequently alluded to in the Greek and Roman classics as the birthplace of Mercury, who from that circumstance is often called Cyllenius. There was a famous temple of that deity on the top of the mountain, which was believed by the ancients to be so high as to be beyond the reach of winds and rain. The modern name of Cyllene is Zyria; and its height, as determined by the French survey, is 7788 feet above the sea. It is thus inferior in height to Taygetus alone of all the mountains in the Morea.