Nemacolin's Path or more often Nemacolin's Trail was a Native American trail situated to cross the great-barrier of the Allegheny Mountains via the Cumberland Narrows Mountain pass and connect between the Potomac River and the Monongahela River watersheds on either side of the Allegheny range of the USA. Nemacolin's Trail thus connected Cumberland, Maryland with what became Brownsville, Pennsylvania. It was an ancient Indian trail, and when improved around 1750 became the template trail, in large part the actual route for what became known on the eastern slopes as the eastern part of Braddock's Road, and which later evolved into the Cumberland Road, and the National Road, then the National Pike, and eventually U.S. Route 40, the so-called National Highway. To complete its historical impact, U.S. Route 40 became one of the first officially recognized highways in the United Statesand the earlier road, the Cumberland Road/National Road was the road on which the first cast iron bridge in the United States was constructed. The trail became the gateway by which settlers in Conestoga Wagons, or by stage coach were able to reach the promised lands of the American near and far west.

The trail is of immense historical importance as crossing the Allegheny divide was a major task taking much planning, time and effort until well into the twentieth century as evidenced by the lack of east-west highways for the length of the border between Virginia and West Virginiathe two regions sundered by some of the harshest terrain in the mountain chain. Crossing the Allegheny range to the north of the Cumberland Gap or to the south is feasible only hundreds of miles to either the north or south as its ridgelines are oriented north-south presenting a virtually impassible obstacle to east-west travel.

Nemacolin's Path starts from a site in present day Cumberland, Maryland, continuing on to Brownsville, Pennsylvania to the neighborhood known today as Redstone located at mouth of Redstone Creek, and known formerly in colonial America as Redstone Old Fort. During 1749 and 1750, the trail was cleared by the Delaware Indian chief Nemacolin and Maryland frontiersman Thomas Cresap.

Later, during the French and Indian War, the eastern part of Nemacolin's path was used as military route for General Edward Braddock's ill-fated attempt to capture Fort Duquesne which among other reasons, was forestalled by the capture of the force under Colonel George Washington at Fort Necessity where he was staging supplies for a move down to the western trail head and crossing point on the Monongahela at Redstone Creek (now Brownsville, Pennsylvania).