The linguistic phenomenon is comparable to that of h-dropping in dialects of Modern English and to the development by which /h/ was lost in late Latin.
[2] In Attic, there was widespread variation in popular speech during the classical period,[3] but the formal standard language retained /h/.
[4] Alexandrine grammarians codified Greek orthography during the 2nd and 1st centuries BC and introduced, among other things, the signs for the rough ( ῾ ) and smooth ( ᾿ ) breathings, to make the distinction between words with and without initial /h/.
By the late Roman and early Byzantine period, /h/ had been lost in all forms of the language.
In the polytonic orthography that started in the Hellenistic period of Ancient Greek, the original /h/ sound, where it used to occur, is represented by a diacritic ( ῾ ), called the rough breathing or spiritus asper.