Many local variants of the Greek alphabet were employed in ancient Greece during the archaic and early classical periods, until around 400 BCE, when they were replaced by the classical 24 letter alphabet that is the standard today. All forms of the Greek alphabet were originally based on the shared inventory of the 22 symbols of the Phoenician alphabet, with the exception of the letter Samekh, whose Greek counterpart Xi (Ξ) was used only in a sub-group of Greek alphabets, and with the common addition of Upsilon (Υ) for the vowel /u, ū/. The local, so-called epichoric, alphabets differed in many ways: in the use of the consonant symbols Χ, Φ and Ψ; in the use of the innovative long vowel letters (Ω and Η), in the absence or presence of Η in its original consonant function (/h/); in the use