An Act of Congress in 1806 authorizing construction of the National Road required mile markers at regular intervals to reassure travelers 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 examples appeared in the fourth century B.C. on the Appian Way from Rome to Brindisi. Along the National Road, markers were set at one-mile intervals on the north side of the road. Although each state's markers had a different design, they all displayed the same information. In Ohio, the markers were square with round heads and made of an early form of concrete, sandstone, or limestone, while in Pennsylvania they were obelisks of cast iron. Ohio's five-foot-tall markers were set two feet into the ground with three feet exposed. Each marker gave the distance from Cumberland, Maryland, where the road begins, and the name and mileage to the nearest cities and villages for eastbound and westbound travelers. The top showed the number of miles from Cumberland, the next row named the next big town and the miles to it, the left side gave eastbound travelers the next big town to the east, and the right side gave westbound travelers the next big town to the west and the miles remaining. At the lowest level, an initial and a small number usually identified the nearest town, recognizable to local people without spelling it out. By the 1920's, a uniform highway numbering system and standardized road signs had replaced the old mile markers, though many still remain along the road.