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 of the Stoudion monastery in Constantinople. The earliest type of books written in minuscule, dated from the mid-9th to mid-10th century, are called codices vetustissimi ('oldest codices'). During the following centuries, this style of writing was further developed and took on more cursive elements again. This became the dominant type of handwriting until the post-Byzantine period. Together with the minuscule letter shapes, Greek writing also began to use word-boundary spaces and diacritics (i.e. the accent marks and breathings of polytonic orthography) more regularly. Some punctuation began also to be employed. The iota subscript was employed from the 13th century onwards.