In the long extension of the Nile Valley, approximately 1000 km (621 miles) from north to south, the existence of dialectal varieties has always been assumed. The old writing system, however, the Hieroglyphs and their subsequent cursive developments (Hieratic and Demotic), concealed these mostly by not marking the vowels. Though dialectal features are detectable in Demonic-Egyptian, only the use of the Greek alphabet for writing Coptic-Egyptian unveiled clearly the differences in the vocalic and consonants structure of a number of dialects.
Modern linguistic research discern six mayor dialect groups: Akhmimic, Lycopolitan, Mesokemic, Fayyumic, Sahidic, and Bohairic, all of which also show some sub-varieties. Only Sahidic and Bohairic were in use as literary and liturgical languages all over Egypt and for a longer period of time.