bilabial plosive pronunciation and eta was a long open-mid front vowel. Onomatopoeic verbs such as for the lowing of cattle (cf. Latin ), for the roaring of lions (cf. Latin ) and as the name of the cuckoo (cf. Latin ) suggest an archaic pronunciation of long upsilon, before this vowel was fronted to . Morpho-phonological facts Sounds undergo regular changes, such as assimilation or dissimilation, in certain environments within words, which are sometimes indicated in writing. These can be used to reconstruct the nature of the sounds involved. <> at the end of some words are regularly changed to <> when preceding a rough breathing in the next word. Thus, e.g.: for or for . <> at the end of the first member of composite words are regularly changed to <> when preceding a spiritus asper in the next member of the composite word. Thus e.g.: The Attic dialect in particular is marked by contractions: two vowels without an intervening consonant were merged in a single syllable; for instance uncontracted (disyllabic) () occurs regularly in dialects but contracts to in Attic, supporting the view that was pronounced (intermediate between and ) rather than as in Modern Greek. Similarly, uncontracted , () occur regularly in Ionic but contract to and in Attic, suggesting values for the spurious diphthongs and in Attic as opposed to the [i] and [u] sounds they later acquired. Non-standard spellings Morphophonological alternations like the above are often treated differently in non-standard spellings than in standardised literary spelling. This may lead to doubts about the representativeness of the literary dialect and may in some cases force slightly different reconstructions than if one were only to take the literary texts of the high standard language into account. Thus, e.g.: non-standard epigraphical spelling sometimes indicates assimilation of final to before voiced consonants in a following word, or of final to before aspirated sounds, in words like . Metrical evidence The metres used in Classical Greek poetry are based on the patterns of light and heavy syllables, and can thus sometimes provide evidence as to the length of vowels where this is not evident from the orthography. By the 4th century AD poetry was normally written using stress-based metres, suggesting that the distinctions between long and short vowels had been lost by then, and the pitch accent had been replaced by a stress accent. External evidence Orthoepic descriptions Some ancient