(κύαθος, a cup), in Antiquity, a common measure among the Greeks and Romans. It was equal to one-twelfth of the sextarius, or of a pint English, and was used as a measure of things both of the liquid and dry kind. The cyathus frequently occurs as the name of a drinking-vessel used by the Romans; in which case it was made with a handle, like the modern ladle. With this vessel the drinking-cups at a banquet were supplied from the mixing-bowl by a slave. The cyathus is referred to as the measure of the quantity drank by a person on such occasions; and it was a common practice at convivial meetings to make the number of cyathi correspond to the number of the muses, or to that of the letters in a patron's name—a kind of compliment not very dissimilar to the modern practice of drinking a person's health. The word cyathus also denoted a cupping-glass; and it was likewise used to signify the hollow of the hand.

CYAXARES I., the son of Phraortes, and third king of Media, reigned B.C. 634—594. See MEDIA.

CYAXARES II., an ancient Persian king, mentioned by Xenophon. Some identify him with Darius the Mede of Scripture, others deny his existence altogether.