It was a Tuesday when construction workers found it. The location was lower Manhattan and the year was 2010 — nine years after the attacks of Sept. 11, 2001, that toppled the World Trade Center towers.

The workers were in awe. Underneath the black muck and ooze of the ruins lay an exoskeleton of something that hadn’t seen air for 200 years and, freshly exposed to the elements, was quickly deteriorating.

It was a vessel, 30 feet long. Hundreds of years old, the cargo ship had somehow been preserved 20 to 30 feet below street level — below what had once been the tallest buildings on the planet. Pictures show baffled men clad in orange hovering around the ship like fossil hunters at an excavation.

“We’re trying to record it as quickly as possible,” Doug Mackey, a chief regional archaeologist for the New York State Office of Parks, Recreation and Historic Preservation, told the New York Times. “And do the analysis later.”

Much of the analysis has now been done. Columbia University researchers laid out many of the ship’s secrets in a fresh study published this month in the journal Tree-Ring Research. And not only does the research show where the ship came from, but scientists say this “rare and valuable piece of American shipbuilding history” helps shed light on how ships of that period were constructed.

The land upon which the World Trade Center was built was not always land. And New York City was not always New York City. In 1647, the Dutch West India Company built the first wharves in what was then New Amsterdam. After the British came to town and founded New York, some of the coastline and inland bodies of water were filled to create more land. Even back then, apparently, real estate in lower Manhattan was hot.

“Cheap and abundant fill materials such as rocks, earth and refuse were placed behind wooden barriers or within wood structures to create new land,” the study states. “Earlier wharfs and abandoned merchant ships were often a component of the fill in newly constructed land.”

Sometime between 1760 and 1818, the study says, the land where the World Trade Center would stand was filled. “The location where the ship was found had been infilled by the 1790s,” wrote the scientists, led by Dario Martin-Benito of Columbia’s Tree-Ring Laboratory. “Our hypothesis is that the ship was built in the mid to late 18th century and was sunk, either deliberately or accidentally, less than thirty years later.”

But where was it built? And by whom?

The answers, researchers say, are in its wood. Applying the techniques of dendrochronology, or tree-ring dating, the researchers homed in on what went down — and where. “What makes the tree-ring patterns in a certain region look very similar, in general, is climate,” Martin-Benito explained to Live Science. Local rain levels and temperatures, he said, dictate regional ring patters. The wetter the climate, the thicker the rings.

One major clue was the ship’s keel. It contained hickory, “which greatly reduces the possible provenance to the eastern United States or to East Asia, the latter of which is unlikely.”

The most likely area: Philadelphia. Their research “suggests that most if not all of the timbers used to build the ship came from the same forest in the Philadelphia area.”

That finding, researchers said, supports earlier theories that the ship, because of “certain idiosyncratic aspects of the vessel’s construction,” had been built at a “small rural shipyard rather than a large, established, and well-financed shipyard.”

It just so happens that shipbuilding was one of the most important industries at that time in eastern Pennsylvania and Philadelphia, where colonials constructed ships of similar size and makeup.

So what brought down the ship? The study said it sank at a lower Manhattan harbor only 20 to 30 years after it was built and may have made at least one trip to the Caribbean. But its “short lifespan,” was perhaps due to “hard use, repairs and shipworm infestation.”

“I don’t know much about the life expectancy for boats,” Martin-Benito told Live Science. “But that doesn’t seem like too long for something that would take so long to build.”