Born of the Patuxent River and then destroyed by it, the mill town Triadelphia knew years of glory as a leading Maryland industrial center. Triadelphia ("three brothers") was founded in 1809 by brothers-in-law Thomas Moore, Isaac Briggs, and Caleb Bentley, who married Brooke sisters. Its water wheels powered a cotton spinning mill with six carding engines and 444 spindles, a sawmill, grist mill, and mill for grinding bone and plaster. Around the mills sprang up a structured little city: smithy, cooperage, wheelwright shop, stables, church, cotton factory, company store, post office, cabinet shop, orchard, garden area, meat house, lime kiln, school house, Odd Fellows Hall, 15 detached houses and 11 double houses.

Triadelphia's golden years came after 1840, when Thomas Lansdale took over the factory and mills. The town throbbed with 400 people. Straining eight-horse teams brought wagonloads of raw cotton and supplies from Baltimore and returned laden with muslin, products of the grist mill, and cotton duck for making ship sails.

Then came a train of disasters. The Civil War strangled the flow of southern cotton. An 1868 flood swept away houses. The end came in the 1889 deluge that also caused the Johnstown flood. Richard H. Lansdale, a grandson of Thomas and future miller, recalled walking as a child away from the wrecked town with a pillow under one arm and a chicken under the other. Today Triadelphia's foundations slumber beneath the reservoir that bears its name.

The company store with its stark stone facade stood among Triadelphia's last buildings. Wrote Charles H. Brooke of the carefully planned mill town: "The factory, mill and store and farm were busy and a large tenantry could hear the hum of machinery from morning till night. The business was like clockwork in every branch, perfect systems prevailing everywhere."