An act of Congress in 1806 authorizing construction of the National Road required mile markers at regular intervals to reassure travelers that they were on the correct route and to show distance traveled and distance to destinations. The practice of using mile markers began in the Roman Empire with stone obelisks, and the first Roman mile markers appeared in the fourth century B.C. on the Appian Way from Rome to Brindisi. Along the National Road, markers were set at 1 mile intervals on the north side of the road. Each state used a different design but displayed the same information: Ohio's were square with round heads and made of an early form of concrete, sandstone, or limestone, while Pennsylvania's were cast-iron obelisks. Ohio's 5-foot markers were set 2 feet deep with 3 feet exposed. The markers showed the number of miles from Cumberland, Maryland, where the road begins, the name and mileage of the next large town, destinations for eastbound travelers on the left and westbound travelers on the right, and usually an initial and small number at the bottom indicating the nearest town. By the 1920s, a uniform highway numbering system and standardized road signs had replaced the old mile markers, though many still remain along the road.
