In 1791, Captain Jonathan Devol, acting on a proposal from Griffin Greene, designed and built a floating grain mill on two boats anchored a few yards from the Ohio River shore. Oak planks fastened the boats together and formed a deck supporting a frame building that enclosed the mill's running gears and millstones. Positioned in a rapid part of the river near Farmer's Castle, a fortification of thirteen blockhouses built by local farmers at the beginning of the Indian Wars, the mill was shielded from Indian raids. The river's current turned the mill wheel, and, depending on the current's strength, the mill processed between twenty-five and fifty bushels of grain in twenty-four hours. It replaced the hand mill, which had become too laborious to operate, and supplied meal to the garrison at Farmer's Castle and to settlers along nearly thirty miles of the Ohio River.