Originally, based on an incorrect map, the royal charter granted Maryland the Potomac River and territory northward to the fortieth parallel. This was found to be a problem, because the northern boundary would put Philadelphia, the major city in Pennsylvania, within Maryland. The Calvert family, which controlled Maryland, and the Penn family, which controlled Pennsylvania, engaged two surveyors, Charles Mason and Jeremiah Dixon, to survey what became known as the Mason-Dixon line which would form the boundary between their two colonies.
St. Mary's City was the largest site of the original Maryland colony, and was the seat of state government until just before the beginning of the 18th century (when the government was moved to Annapolis). The government was moved at about the same time as the persecution of Maryland Catholics by Puritans from Virginia; during the persecutions, all of the original Catholic churches of southern Maryland were burned down. St Mary's City is now an archaelogical site, with a small tourist center.
Maryland's main airport is Baltimore-Washington International Airport (formerly known as Friendship Airport). The Maryland suburbs of Washington, D.C. are also serviced by the other two airports in the region, Reagan National and Dulles International Airports, both in Virginia.