Cannonball on Governors Island

The approximately 12inch diameter cannonball found on Governors Island via Governors Island Blog

On Thursday, a cannonball caused a stir on Governors Island when it was found in a construction site. Since the object may have been dangerous, the FDNY and NYPD bomb squad hopped on the Governors Island ferry and rode over to the island to make sure no one was in danger.

This morning, while doing construction work near Soissons Dock, workers found an old cannon ball near the seawall. NYPD came out to assess the cannonball and determined that it was a solid shot made of iron and contained no explosive material.
- Governors Island Blog

DNAinfo has more info on the cannonball response.