In a small survey boat, maritime archaeologist J. Lee Cox Jr. was checking the bottom of the Delaware River at the Sunoco Logistics pier in South Philadelphia when he got a hit on the side-scan sonar. A pipe? A log? A hazard to the oil tankers docking nearby?

No one was sure until a diver was sent down weeks later and found a strange pointed object buried in the muck about 40 feet down.

Earlier this month, Cox identified it as the business end of a cheval-de-frise, an iron-tipped log once embedded in the river, along with many others, to gore the hulls of British warships menacing Philadelphia in the mid-1770s. It had been silently resting not far from where oil-laden Sunoco tankers have berthed since Philadelphia's industrial age.