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 for Semitic languages, and these "matres lectionis", as well as several Phoenician letters which represented consonants not present in Greek, were adapted according to the acrophonic principle to represent Greek vowels consistently, if not unambiguously. The Greek alphabet was developed by a Greek with first-hand experience of contemporary Phoenician script. Almost as quickly as it was established in the Greek mainland, it was rapidly re-exported, eastwards to Phrygia, where a similar script was devised. It was also exported westwards with Euboean or West Greek traders, where the Etruscans adapted the Greek alphabet to their own language, which eventually led to