The word itself originated in the 18th century when archaeologists studying ancient Roman ruins noticed scratched inscriptions on walls. They were impressed by the sheer number of these markings, calling them "graffiti" to describe the act of scratching, and the resulting markings themselves.
So, while "graffiti" is now associated with modern street art, it actually originated from a word describing ancient forms of inscription. The meaning has evolved, but the core idea of marking surfaces with scratches and words has remained constant.