Earlier quoted context omitted.
I wonder how many places have the geology for these massive stone walls that can be carved and ... folks saw it and thought "Man we should make this really big sculpture!". My imagination makes me think that it's a pretty obvious thing to do for any number of reasons and that there have been quite a few that have been lost to time.
As evidenced by the amount of grafitti in public places, people just really like leaving their mark wherever they can. There's grafitti in ancient ruins that (aside from the language) could be mistaken for grafitti in a bathroom stall. People are just gonna people.
Wonderful slice of some potter rivalry from long long ago ;)