When did the Romans start using Z?

Question

Several of my recent questions have touched on the letter Z, which was introduced fairly late to the alphabet (it's disappeared from its Phoenician position and been added back in at the end, in its Greek form).

Clearly it wasn't in common use in Plautus's time, since he uses ss to transcribe zeta in Greek loans. On the other hand, some manuscripts of Plautus contain the word zona for (non-Attic) Greek ζώνα. Etruscan used the letter for a native affricate, but generally in a different shape from the Greek form with the slant in the middle.

When did the letter Z first start re-appearing in Latin? And when did it catch on, if ever? In other words, when did Greek loans commonly start to use Z for zeta instead of S or SS?

(Note that I'm not interested in the archaic use for the sound that rhotacized into /r/. Instead, I'm wondering about when it was borrowed back from Greek.)

Answer 1

The letter Z began to again be used shortly after the conquest of Greece (late 2nd century BC, early 1st century BC), but did not see a "formal" introduction into the Latin alphabet until later, as described by Cicero, Quintilian, and others.

After the conquest of Greece in the first century BC, Z (and Y) was reintroduced into Latin but only to convey the sound of zeta in transliterated Greek loan-words. Even though the letter then was in use, sources such as Quintilian (and Cicero, De Natura Deorum, II.93) demonstrate that its formal placement in the alphabet did not occur until later. When it did, the letter Z (together with Y) was relegated to the end of the alphabet, its original place having been taken by G.

The above text was taken from here; additional citations can be found at the bottom of the page here: http://penelope.uchicago.edu/~grout/encyclopaedia_romana/miscellanea/zed.html