How often is it that archaeologists come across ancient Roman ruins with Latin writing/graffiti that doesn't need to be restored OR is perfectly legible? Similarly, how often often is it that one will come across very well preserved mosaics or artwork?
I have been on digs in the past. One one, we find lots of colored pieces of mosaics at the bottom of what was a Roman drainage system. This suggests that a building nearby had a beautiful mosaic floor at one time (we have found blue, red, green, yellow, black and gold). It is very rare to come across a completely intact mosaic. However, you can see great examples of these in places like Pompeii and Ostia that have been preserved due to outside circumstances (Pompeii from Vesuvius, Ostia from flooding of the Tiber and subsequent siltation). Similarly, graffiti was common in Roman times and we often find bits and pieces. Just like a mosaic, it's rare and exciting to come across a totally intact piece (Pompeii is full of it though). Graffiti was often etched into buildings, meaning restoration is not too terribly difficult.