The now-lost city of Triadelphia (“three brothers”) was founded in 1809 by brothers-in-law Thomas Moore, Isaac Briggs, and Caleb Bentley. The three men were married to the Brooke sisters, who were descendants of Robert Brooke– the founder of nearby Brookeville in Montgomery County.
According to the Sandy Spring Museum, Triadelphia was a mill town “born of the Patuxent River and then destroyed by it.” From its founding until the Civil War, the Patuxent River, which today marks the northeastern border of Montgomery County, powered the mills that made Triadelphia a thriving industrial community. At its peak, the town was even larger than nearby Rockville.
As planned, the town’s cotton, grist, saw, and plaster mills were all powered by the river. It was the only town of its kind in Montgomery County, though nearby cities like Ellicott City were formed with the same purpose. So what happened to Triadelphia? The same water that helped create the thriving town also ended up destroying it. A devastating flood in 1868 caused significant damage, sweeping away homes and destroying nearly every mill except for the grist mill…