Editing Mason–Dixon line (section)

==Background==
{{main|Penn–Calvert boundary dispute}}
[[File:Mason-Dixon Survey Historical Marker Front and South Sts Philadelphia PA (DSC 3153).jpg|thumb|A historical marker at [[Front Street (Philadelphia)|Front]] and [[South Street (Philadelphia)|South]] streets in [[Philadelphia]], where the survey began]]
[[History of Maryland#Colonial Maryland|Maryland's charter]] of 1632 granted [[Cecil Calvert, 2nd Baron Baltimore|Cecil Calvert]] land north of the entire length of the [[Potomac River]] up to the [[40th parallel north|40th parallel]].<ref name="msa">{{cite web|url=http://msa.maryland.gov/megafile/msa/speccol/sc6000/sc6046/000000/000001/000000/000007/pdf/msa_sc6046_1_7.pdf |title=Maryland Geological Survey, Volume 7 |publisher=Maryland State Archives |access-date=2015-03-20}} See section "History of the Boundary Dispute Between the Baltimores and Penns Resulting in the Original Mason and Dixon Line" by Edward Bennett Matthews</ref> A problem arose when [[Charles II of England|Charles II]] granted a [[History of Pennsylvania#Province_of_Pennsylvania|charter for Pennsylvania]] in 1681. The grant defined Pennsylvania's southern border as identical to Maryland's northern border, but described it differently, as Charles relied on an inaccurate map. The terms of the grant clearly indicate that Charles II and [[William Penn]] believed the 40th parallel would intersect the [[Twelve-Mile Circle]] around [[New Castle, Delaware]], when in fact it falls north of the original boundaries of the City of [[Philadelphia]], the site of which [[William Penn|Penn]] had already selected for his colony's capital city. Negotiations ensued after the problem was discovered in 1681. A compromise proposed by Charles II in 1682, which might have resolved the issue, was undermined by Penn receiving the additional grant of the "Three Lower Counties" along [[Delaware Bay]], which later became the [[Delaware Colony]], a satellite of Pennsylvania. Maryland considered these lands part of its original grant.<ref name=hubbard>{{cite book |last= Hubbard | first= Bill Jr. |title= American Boundaries: the Nation, the States, the Rectangular Survey |year= 2009 |publisher= University of Chicago Press |isbn= 978-0226355917 |pages= 20–29}}</ref>

The conflict became more of an issue when settlement extended into the interior of the colonies. In 1732, the [[Proprietary Governor]] of Maryland, [[Charles Calvert, 5th Baron Baltimore]], signed a provisional agreement with [[William Penn]]'s sons, which drew a line somewhere in between and renounced the Calvert claim to Delaware. But later, Lord Baltimore claimed that the document he had signed did not contain the terms he had agreed to, and refused to put the agreement into effect. Beginning in the mid-1730s, violence erupted between settlers claiming various loyalties to Maryland and Pennsylvania. The border conflict would be known as [[Cresap's War]].<ref name=expansion>{{cite journal|url=https://journals.psu.edu/phj/article/view/24559/24328|author=Paul Doutrich|title=Cresap's War: Expansion and Conflict in the Susquehanna Valley|journal=Pennsylvania History|volume=53|date=1986|pages=89–104|publisher=Cip.cornell.edu}}</ref>

Progress was made after a [[Court of Chancery]] ruling affirming the 1732 agreement, but the issue remained unresolved until [[Frederick Calvert, 6th Baron Baltimore]] ceased contesting the claims on the Maryland side and accepted the earlier agreements. Maryland's border with Delaware was to be based on the [[Transpeninsular Line]] and the Twelve-Mile Circle around New Castle. The Pennsylvania–Maryland border was defined as the line of latitude {{convert|15 |miles}} south of the southernmost house in Philadelphia (on what is today [[South Street (Philadelphia)|South Street]]). As part of the settlement, the Penns and Calverts commissioned the English team of [[Charles Mason]] and [[Jeremiah Dixon]] to [[surveying|survey]] the newly established boundaries between the [[Province of Pennsylvania]], the [[Province of Maryland]], and [[Delaware Colony]].<ref name=hubbard/>

In 1779, Pennsylvania and Virginia agreed "To extend Mason's and Dixon's line, due west, five degrees of longitude, to be computed from the river Delaware, for the southern boundary of Pennsylvania, and that a meridian, drawn from the western extremity thereof to the northern limit of the said state, be the western boundary of Pennsylvania for ever."<ref>{{cite book |last=Barton |first=William |title= Memoirs of the life of David Rittenhouse, LLD. F.R.S. |year=1818 |publisher=E. Parker |pages=282–283 |isbn=978-0608436135 |url= https://books.google.com/books?id=_J8RAAAAYAAJ&pg=PA283}}</ref>

After Pennsylvania abolished [[Slavery in the United States|slavery]] in 1781, the east–west part of this line and the [[Ohio River]] became a border between [[slave and free states]],<ref>{{cite web |last=Hudson |first=J. Blaine |title=Crossing the "Dark Line": Fugitive Slaves and the Underground Railroad in Louisville and North Central Kentucky (excerpt) |url=http://www.ket.org/underground/research/crossing.htm |work=KET's Underground Railroad: Passage to Freedom, with Kentucky Humanities Association |access-date=February 25, 2007 |archive-url=https://web.archive.org/web/20130212015127/http://www.ket.org/underground/research/crossing.htm |archive-date=February 12, 2013 |url-status=dead}}</ref> with Delaware<ref>{{cite web |title= Slavery in Delaware |url= http://slavenorth.com/delaware.htm |website= Slavery in the North |access-date=6 October 2015 }}</ref> retaining slavery until the [[Thirteenth Amendment to the United States Constitution|13th Amendment]] was ratified in 1865.