Two archaeologists hired to observe construction work and document artifacts at New York City's Ground Zero made an amazing discovery Tuesday night.

A 32-foot piece of an 18th century ship was found buried 20 feet below the street where the World Trade Center towers once stood. It was uncovered by a crew excavating the site for a new parking garage

No one is really sure how it got there. Archaeologists said the vessel may have been used as filler to extend lower Manhattan into the Hudson River more than 200 years ago.

"It was apparently somewhat common to sink ships in landfill as people were building land further out into the Hudson River and the East River, but only a handful of these ships have been found so far, so it is really quite rare," explained Molly McDonald with AKRF Consulting. It is just exciting to find it here on the World Trade Center site."

A 100-pound iron anchor was found a few yards from the hull, possibly from the old vessel.

Conservation specialists have been carefully trying to salvage some of the wood from the boat, but exposure to the air could cause it to deteriorate.

Historians say the ship may date to the 1700s. Timber samples will be sent to a laboratory where scientists hope to find out at least when it was constructed.