The Treaty of York was signed by Henry III of England and Alexander II of Scotland on the 25th of September, 1237.
Scotland is one of the four constituent countries of the United Kingdom, occupying the northern third of the island of Great Britain and, apart from the mainland, Scotland consists of over seven hundred and ninety islands. It is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the southwest. Scotland's only land border is with England, which runs for sixty miles (ninety-six kilometres) between the mouth of the River Tweed on the east coast and the Solway Firth in the west, mostly using rivers, mountain ridges and other natural features. Scotland’s national borders also comprise sea borders; two with England and several with other countries. The western sea border with England extends seaward from the Solway Firth, whereas the eastern border extends into the North Sea from the mouth of the River Tweed.
The border between Scotland and England was officially defined for the first time and by mutual agreement through the Treaty of York. It was signed in York by King Henry III of England and Alexander I of Scotland on the 25th of September, 1237. The signing of the treaty was one of the major events of the reign of Alexander I. The border it defined was essentially the one that exists to this day. So to a large extent, the boundaries of Scotland were established by that Treaty of York, the 1266 Treaty of Perth between Scotland and Norway, and by the 15th Century acquisitions of Orkney and Shetland from Norway. Exceptions to that statement include the Isle of Man, which is now a crown dependency outside the United Kingdom, and the small rocky islet of Rockall in the North Atlantic, which was annexed by the UK in 1955 and later declared part of Scotland by the Island of Rockall Act of 1972. In addition, there was a sort of tidying-up arrangement between Scotland and England in 1552, during the time of Mary Queen of Scots. That was related to the largely featureless ‘Debateable Lands’ between the rivers Sark and Esk in the west, but otherwise the border hasn’t been altered in almost eight centuries.
In addition to defining the border, the treaty addressed other issues between the two Kings who had a bit of a history of making agreements with each other. Henry and Alexander were brothers-in-law as the Scottish King had married Henry’s sister Joan. The treaty was witnessed by a Papal Legate called Otho and it was written in Latin and entitled ‘Scriptum cirographatum inter Henricum Regem Anglie et Alexandrum Regem Scocie de comitatu Northumbrie Cumbrie et Westmerland factum coram Ottone Legato’. It could have been known as the ‘Treaty with the long name’ and it was signed and agreed in respect of “all claims, …up to Friday next before Michaelmas A.D. 1237.” Those other issues and claims related to Alexander’s and his predecessors’ attempts to extend Scotland’s frontier southward into England.
As it happened, the Kings of Scotland had long-standing claims to the territories of Cumberland, Northumberland and Westmorland, with David I having ruled over large tracts of those lands in the 12th Century. In fact, David I died at Carlisle, where he had spent a lot of his time. William I, David’s grandson, had acknowledged Henry II as his feudal lord in 1174, but that was largely ignored and for most of the 13th Century, Scotland retained much of its freedom and independence if not its influence in those northern parts. However, there at York in 1237, Alexander II gave up any claim to those northern counties in exchange for certain estates within them, notably in Tynedale and at Penrith, for which he swore fealty to the English King. Those estates were to be held by Alexander and his successors with certain hereditary rights and freedoms, including the prevalence of Scots Law, and the exemption of the Scottish King and all his future heirs from English Law, in those territories. In addition to the giving up of that territorial advantage, Alexander relinquished Scotland’s claim to a refund of 15,000 marks, which was due as a result of King John’s having reneged on a past arrangement with William the Lion. Never trust a medieval Englishman.
As regards border disputes, Berwick on Tweed was the subject of dispute for another two centuries after the Treaty of York was signed. The English invaded Scotland and unlawfully occupied the Scottish Royal Burgh of Berwick on Tweed on a number of occasions between 1296 and 1482. Berwick had received its founding royal charter from David I in 1124 and the Treaty of York, which has never been rescinded or repealed, in no way amended Berwick’s Scottish status. On the contrary, by its definition of the border, the treaty confirmed Berwick as being in Scotland. After Berwick was unlawfully annexed by England in 1482, there came a compromise of sorts via the 1502 Treaty of Perpetual Peace, which left Berwick under English administration, whilst it remained part of Scotland and subject to Scots Law. The Tweed border defined by the earlier Treaty of York was not altered and even after the Treaty of Union of 1707, there was no change to the border or the application of Scots Law.
That situation lasted until the Wales and Berwick Act of 1746, which unconstitutionally ordained that henceforth English Law would apply in Berwick-upon-Tweed. Significantly, that act did not incorporate Berwick into England and, in truth it wasn’t much more than a panicky reaction to the 1745/46 Jacobite Rising. That 1746 act was repealed by the fairly recent Interpretation Act of 1978, but nevertheless, Berwick remains a separate enclave under administration by the English County of Northumberland. Importantly, however, the administrative boundary near Lamberton does not represent the border, which remains as per the Treaty of York.
Incidentally, Berwick's football team plays in the Scottish league and in 2008, a poll of Berwick’s population showed that eighty per cent would prefer to come under Scottish administration. The fact is that they are in Scotland and the administration remains an unconstitutional anomaly. A final titbit for you is that the A1237 near York was so named after the date of the Treaty of York.