The ruins of ancient, multi-story stone buildings stand near Farmington, New Mexico. It’s called Aztec Ruins National Monument, although it’s a misnomer. Ancestral Puebloans built these about 900 years ago. The largest of these buildings consists of more than 400 masonry rooms. And on the ceilings -- there’s graffiti. Who wrote it, and what does it tell archaeologists about the history of the site? Cortez historian Fred Blackburn is engaged in that research.