Driving down I-95 past South Philly on the way to a game or the airport, you may have noticed a tall brick structure on the right that looks like a giant smokestack. It has a greenish detached cover. You may have wondered, "What is that thing?" and then forgotten about it a second later.

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Turns out that thing is a Philadelphia landmark. And it is not a smokestack. It was once a munitions factory.

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Back before they invented bullets, people used lead balls to shoot things. Those balls (also known as "shot") were originally made in wooden molds, but they were imperfect and could be made only a few at a time. Someone discovered that you could mass-produce perfectly spherical lead balls using a "shot tower."

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Molten lead was poured through a sieve at the top of the tower. The individual lead droplets assumed a perfectly spherical shape as they sailed down and plunked into a vat of water below. The water cooled the droplets and they became shot, suitable for hunting animals, or for ammunition in war.

 

Thomas Sparks, a plumber, built the 140-foot tower in 1808. It was America's first shot tower and proved extremely helpful in supplying ammunition for the War of 1812 and the Civil War.

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The Sparks family ran the tower for generations, but it closed for good after about 100 years. It is now locked up and stands next to a city playground.

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Now you know.