Crews digging a storm water trench on Governor’s Island unearthed the rusty, filthy remains of what appeared to be the remains of a train. They had no idea what it was. But we do.

It’s an archbar, a relic from the days when the island was a key military installation. During World War I, the Army built the Governor’s Island Railroad to move equipment around the 172-acre island, which first housed a colonial militia in 1755. The railroad had just 1.75 miles of track and three flat cars that moved between the pier, shops, and warehouses. That made it the world's shortest railroad, The New York Times said in 1931. The railroad was dismantled that year.

In 1966, the Army handed the island over to the Coast Guard, which maintained a base there for 30 years. The city bought 150 acres of the island in 2003, and the Trust for Governor's Island is now turning it into a park with spaces for non-profit and commercial facilities.

An archbar is a type of freight car truck common in the early 1900s, says Robert Holzweiss, president of the Railway & Locomotive Historical Society. Simply put, they're the wheels the boxcar sits on. They were commonly used on freight and maintenance cars, as well as early tenders and cabooses, according to Don Mooney, president of the Railroad Historical Society of Northern New York. The Association of American Railroads banned the design, which was outdated and required a lot of maintenance, from interchange (railroad to railroad) service in 1939.

Island officials plan to do more research and find a place to display the relic. Why the archbar was sitting underground on the island for nearly a century, we may never know.