I grew up in Pisa and I have been always attracted by the carved inscriptions on the marble walls, here some interesting examples I spotted walking around the cathedral.
Continuing the observation, here's the proof (in my opinion), that to build the Cathedral of marble blocks were used from other buildings. They read Latin inscriptions down on blocks placed in the back side.
So it was not necessary that the markings were clearly legible ... On some marble columns, placed back in the apse, known engraved in the marble of Pisa the symbol of the cross; as well as other more enigmatic crosses. Continuing external observation of the church I see the same (the side facing the Monumental Cemetery), a smaller number of blocks of marble from Roman buildings.
The Latin alphabet that we still use today was created by the Etruscans and the Romans, and derived from the Greek. It had only 23 letters: the J, U and W were missing. The J was represented by the I, the U was written as V and there was no need for a W. The story of the Z is particularly interesting.
In the third century BC, the letter G (a variant of C) was added; Z was borrowed from the Greek, then dropped as Latin had no need for it — perhaps at the behest of the Roman censor Appius Claudius; G took its place in the line-up, until the first century BC, when the Romans decided they needed the Z for borrowed Greek words (when Greek literature became the vogue), they re-introduced it, and placed it at the end of the alphabet, where it remains to this day. Source: http://ilovetypography.com/2010/08/07/where-does-the-alphabet-come-from/
