In 1805, Charles Fenton Mercer had a dam constructed to form a millpond where the bend in Little River approaches the public road to Middleburg. Water from a millpond almost two-thirds of a mile away at the western end of Aldie powered two waterwheels and, in turn, the millstones. Slaves probably dug the millrace and built the wooden gates and wooden flume in the headrace. After powering the merchant mill's pair of overshot wheels, the water flowed through the tailrace and turned the country mill's wheel before rejoining the Little River north of the highway. Today, Aldie's merchant mill is the last standing gristmill in Virginia with tandem overshot waterwheels. Mill workers stopped the waterwheels between grindings by closing the gate to divert the water into an overflow channel, and started them by opening the head gate near the pond so the water could flow down the headrace to the mill.