[AN: Link leads to some things found on Pompeii's walls. Most of it rude. It's not just Pompeii, but also there's a dick drawn on Hadrian's wall, and Nordic runes in a very high place in a cave that read, Gosh this is a long way up, or words to that effect. Humanity never changes.]
They had been excavating for months. The city itself had been flooded by a mudslide in eras past. By all historical accounts, only the most stubborn residents refused to flee before the disaster. In terms of geology, it had gone under very quickly. In less than a week. There had been weeks of warning, and an encroaching tide of mud, all of which only lead to the people living there to ignore all warnings.
Humans could be like that, sometimes. However, there were few left when the most liquid slurry engulfed the area literally overnight. When it was over, there was no trace left and little geography remaining to assist in finding the place. In its own way, it was a time machine. Those excavating it could find the place unchanged for hundreds of years.
Right now, they were finding the graffiti of the public left in public places. Humans were loath to write in their own spaces, but the courtyard of many is also vandalized by everyone. Many a word of wit and wisdom has been left on the surface of a public toilet stall.