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 becoming the first 'true' alphabet. Apparently, some thirty years later, the same alphabet was introduced to Boeotia, having been adopted perhaps a little earlier in Macedonia, and went on in the course of the 4th century to displace the local alphabets throughout the whole Greek-speaking world. The Ionic alphabet included a new letter, omega, at the end of the alphabet, and standardised the representation of various sounds that had varied from one dialect to another, as follows: The absence of a letter for was of no consequence for the Ionic dialects, but sometimes led to ambiguities in Attic, which had