The letter "z" was part of the earliest form of the Latin alphabet, adopted from Etruscan. Because the sound in Latin changed to by rhotacism in the fifth century BC, "z" was dropped and its place given to the new letter "g". In the 1st century BC, "z" was reintroduced at the end of the Latin alphabet to represent the sound of the Greek zeta , as the letter "y" was introduced to represent the sound of the Greek upsilon .