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
Greek alphabet the Thirty Tyrants. Because of Eucleides's role in suggesting the idea to adopt the Ionian alphabet, the standard twenty-four-letter Greek alphabet is sometimes known as the "Eucleidean alphabet". Roughly thirty years later, the Eucleidean alphabet was adopted in Boeotia and it may have been adopted a few years previously in Macedonia. By the end of the fourth century BC, it had displaced local alphabets across the Greek-speaking world to become the standard form of the Greek alphabet. When the Greeks adapted the Phoenician alphabet, they took over not only the letter shapes and sound values, but also the names by