Sparks Shot Tower - Philadelphia, PA - Satellite Imagery Oddities on Waymarking.com

Unlike the shot tower in Baltimore, this one cannot be got to by pedestrians. It was fenced off and had a huge, high, brick wall added to the perimeter for good measure. I could see this a half mile away on my approach. It looks like a smoke stack with a lid on top, but it's really America's first shot tower built in 1808. Shot towers revolutionized the making of musket balls and other solid projectiles based on the principle that molten lead will form perfect round balls when poured from a high place.

Until this discovery, gun shot was made by pouring the lead into wooden molds. Plumber Thomas Sparks and a partner created a 142-foot-high brick tower with a 30-foot circumference at its base tapering to 15 feet at the top. It stands along the Delaware River waterfront at Carpenter Street in South Philly and is easily seen from Route I-95.

The molten lead was poured through a mesh with different sized holes for different sizes of shot. The balls fell into a large container of water. The tower produced tons of ammunition during the War of 1812 and the Civil War. Four generations of the Sparks family kept the tower in operation until 1903. The tower is now part of a city playground with a recreation center at the base. It's a prime example of Philadelphia's reputation for superb brickwork.
SOURCE

The blue PHMP marker outside the perimeter wall reads:

First in the nation. Built 1808 by Thomas Sparks & John Bishop to make hunting shot, it symbolized a new U.S. industrial independence. Bishop, a Quaker, sold his share when ammunition was made here for the War of 1812. The Sparks family stayed in control until 1903