7 Letters of Alphabet

Alpha, (Omicron), Upsilon, Eta, Iota, Beta, Tau
invented by 3 Fates
Invented by Mercury after watching cranes fly
According to Hyginus, the Fates originally invented the initial 7 letters, or the 5 vowels and 2 stops called Alpha, Omicron, Upsilon, Eta, Iota, Beta, and Tau (Α, Ο, Υ, Η, Ι, Β, Τ, or A.B.H.I.O.T.V.). 
Α, Ο, Υ, Η, Ι, Β, Τ,