The historic Mason-Dixon Line is celebrating its 250th birthday with events over the next few years.

English astronomers Charles Mason and Jeremiah Dixon surveyed and marked the line, one of the most famous boundaries in the U.S. The Mason-Dixon Line still serves as a demarcation line, forming part of the borders of Pennsylvania, Maryland, Delaware and West Virginia.

Events will be held at various locations to commemorate the anniversaries of their work. At Mason-Dixon Historical Park in Core, West Virginia, an annual event Sunday will celebrate the surveyors’ work and another historic event of local importance.

The day will begin at 10:30 a.m. with an interactive activity led by a local historian to mark the return of prisoners from the French and Indian War, which ended in 1763, the same year Mr. Mason and Mr. Dixon arrived in Philadelphia. Historical re-enactors will bring to life the political and sociological climate at the time.

Following the presentation, there will be a guided walk to the third and last crossing of Dunkard Creek by Mr. Mason and Mr. Dixon into Greene County. The walk leaves from the parking lot and will be led by Pete Zapadka, founder of exploretheline.com and a retired online editor at the Pittsburgh Post-Gazette.

Participants also will be able to visit the marker atop Brown's Hill, where Mr. Mason and Mr. Dixon were forced to end their survey.

Mr. Zapadka, now of Morgantown, West Virginia, said he became interested in the history of the line while studying geography in high school and has led the hike at the park for the past 10 years.

Though the line has come to symbolize a cultural boundary between the North and the South, Mr. Zapadka said it was the resolution of an 82-year border dispute between British colonies in America. Mr. Mason and Mr. Dixon were commissioned to survey the 233-mile line to define the boundaries of the overlapping land grants of the Penns, proprietors of Pennsylvania, and the Calverts, proprietors of Maryland.

Using astronomical alignments to establish the borders, the surveyors cut a 24-foot-wide line through the wilderness over mountains, into valleys, and across rivers marked by stones every mile and crownstones every 5 miles. They moved west about 2 miles a day and were accompanied by up to 120 people at a time, including 40 ax men, a herd of sheep and a milkmaid.

As for its accuracy, looking at 12 spots where they used astronomical observations, everything is accurate to within 200 feet, and all but one or two are accurate to within 100 feet, Mr. Zapadka said.

Historian Betty Wiley of Westover, West Virginia, grew up near the park where, in her early teens, she said she climbed Brown’s Hill and stood with one foot in Pennsylvania and one in West Virginia. As she grew older, she became fascinated by the history of the line and has been volunteering with the park since the 1970s.

“I think without question, it’s the most famous boundary line in the world,” Ms. Wiley said.

The park owns a copy of the journal that Mr. Mason kept while they were drawing the line, which Ms. Wiley said contains all of their measurements and chronicles what happened every day, including an encounter with an Indian agent who negotiated with representatives of the Six Nations to allow the surveyors to proceed westward.

Upon their agreement, the surveyors were allowed to proceed in peace and were escorted by a company of 11 Mohawks, three Onondagas and an interpreter. According to a journal entry on Oct. 9, 1767, upon the third crossing of the winding Dunkard Creek,  the Indian chief informed them that they could not proceed one step farther westward because they had crossed a warpath, leaving them about 23 miles short of their intended destination.

Mr. Mason and Mr. Dixon continued another 2 miles on their own and established their last marker on top of Brown’s Hill — a 5-foot post with stones piled around it with a “W” marked on the west side. The post was replaced in 1883 by a 3-foot stone marker after a resurvey by Cephas H. Sinclair.

The final 23 miles were completed 14 years later by American scientists Andrew Ellicott and David Rittenhouse.

Though many see the Mason-Dixon Line as a dividing line, Mr. Zapadka has a different view.

“This is the only line that actually doesn’t divide,” he said. “When it was agreed upon, it brought a fledgling nation together.”

For more information, visit www.masondixonhistoricalpark.com. 

First Published: October 16, 2014, 4:00 a.m.