History of the Greek alphabet retained the sound. A symbol based on the left-hand half ( ├ ) of the letter Η was therefore sometimes used to indicate the presence of where necessary, and its absence was indicated by a symbol based on the right half. During the classical period, ΕΙ came to be pronounced and ΟΥ came to be pronounced , Υ having meanwhile moved to . By about 200 BC, a system of diacritical marks was invented, representing the tone accents in use in Ancient Greek. This also helped to indicate the length of the vowels Α, Ι, and Υ in certain cases
History of the alphabet that are not used as national scripts today, a few are clearly independent in their letter forms. The Zhuyin phonetic alphabet derives from Chinese characters. The Santali alphabet of eastern India appears to be based on traditional symbols such as "danger" and "meeting place", as well as pictographs invented by its creator. (The names of the Santali letters are related to the sound they represent through the acrophonic principle, as in the original alphabet, but it is the "final" consonant or vowel of the name that the letter represents: "le" "swelling" represents "e", while "en" "thresh grain" represents "n".) In