History & local legend
Roberts Mill stood beside Mill Creek in Lower Merion, where John Roberts III built a grain mill in 1746. During the Revolution, a story spread that flour from the mill had been mixed with ground glass to poison American soldiers. That accusation gave the site its grim nickname, Ground Glass Mill. Roberts was tried for treason and hanged in Philadelphia in 1778.
The ghost story places a man in colonial clothing in the miller’s house. Some versions identify him as Roberts; others call him Fishburn, a man supposedly killed by a mob that mistook him for the mill owner. By 1894 the poisoned-flour story had traveled across the country: earth from the mill was sent to a Liberty Tree planting in San Francisco with a written account of the tale.
Sources
- Ground Glass Mill, h2g2, Lower Merion’s ghost and its rival identities
- Lower Merion Historical Society, Roberts Mill and the November 1778 hanging in Philadelphia
- Daughters of the American Revolution, Sequoia Chapter, 1894 Liberty Tree planting, p. 22, soil from Roberts’s mill and the ground-glass tale
- Mill Creek Historic District, National Register description, distinct homes of John Roberts III and his grandfather
- Lower Merion Township, Mill Creek Historic District building map
- Lower Merion Historical Society, mill complex and misidentified postcard house