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 Greek alphabet them from certain digraphs which had become homophonous, as follows: The letters of the alphabet were used in the system of Greek numerals. For this purpose the letters digamma and qoppa (but not san) were retained although they had gone out of general use, and the obscure letter sampi was added at the end of the alphabet. Digamma was often replaced in numerical use by stigma (Ϛ), originally a ligature of sigma and tau, or even the sequence sigma-tau (στ'). The Old Italic and Anatolian alphabets are, like the Greek alphabet, attested from the 8th century BC. It is unclear