These stones are the ghosts of a forgotten era in Queens history, entombed in a shabby sidewalk.
They come from a grist mill built in Dutch Kills around 1657 that helped turn the economic fortunes of western Queens.
The Colonial-era relics, among the oldest European artifacts in the borough, are cemented into a sidewalk along Queens Plaza, with only their tops visible.
"People walk on them every single day, and I'm sure they think that they are manhole covers," said Debbie Van Cura, of Long Island City, who teaches sociology at LaGuardia Community College.
"Nobody really understands fully what they are."
That will soon change.
The millstones will be disinterred and displayed in a park to be created along Northern Blvd. as part of a $43 million city project to overhaul the traffic-choked plaza.
Ancient millstones grist for historians