Alexandria, and Aristophanes of Byzantium is said to have invented them. There are three: the acute, circumflex, and grave . The shape of the circumflex is a merging of the acute and grave. The acute represented high or rising pitch, the circumflex represented falling pitch, but what the grave represented is uncertain. Early on, the grave was used on every syllable without an acute or circumflex. Here the grave marked all unaccented syllables, which had lower pitch than the accented syllable. Later on, a grave was only used to replace a final acute before another full word; the acute was kept before an enclitic or at the end of a phrase. This usage was standardized in the Byzantine era, and is used in modern editions of Ancient Greek texts. Here it might mark a lowered version of a high-pitched syllable. ('there is something beautiful') ( is at the end of the sentence) ('it is beautiful') ( here is an enclitic) ('good and beautiful') Sound changes Greek underwent many sound changes. Some occurred between Proto-Indo-European (PIE) and Proto-Greek (PGr), some between the Mycenaean Greek and Ancient Greek periods, which are separated by about 300 years (the Greek Dark Ages), and some during the Koine Greek period. Some sound changes occurred only in particular Ancient Greek dialects, not in others, and certain dialects, such as Boeotian and Laconian, underwent sound changes similar to the ones that occurred later in Koine. This section primarily describes sound changes that occurred between the Mycenaean and Ancient Greek periods and during the Ancient Greek period. For sound changes occurring in Proto-Greek and in Koine Greek, see and Koine Greek phonology. Debuccalization In Proto-Greek, the PIE sibilant became by debuccalization in many cases. PIE > ('the') () — compare Sanskrit PIE > ('seven') — compare Latin , Sanskrit sapta Clusters of and a sonorant (liquid or nasal) at the beginning of a word became a voiceless resonant in some forms of Archaic Greek. Voiceless remained in Attic at the beginning of words, and became the regular allophone of in this position; voiceless merged with ; and the rest of the voiceless resonants merged with the voiced resonants. PIE > > Attic ('flow') — compare Sanskrit () PIE > Corfu (), Attic ('stream') PIE > Pamphylian , Attic () PIE > Corfu , Attic ('taking') () PIE remained in clusters with stops and at the end of a