Spanish) instead of "frontier" or "border", since it does not acknowledge the possibility of having a frontier with what Spain considers to be its own territory. British position The United Kingdom relies on de facto arguments of possession by prescription in relation to the southern part of the isthmus, as there has been "continuous possession [of the isthmus] over a long period". On December 2, 1987, in a joint British-Spanish declaration about the use of the airport, as well as in several EU acts, the UK has acknowledged that Spain disputes the sovereignty of the isthmus (The ... arrangements ... are understood to be without prejudice to the respective legal positions of Spain and the United Kingdom with regard to the dispute over sovereignty over the territory in which the airport is situated.), although they reject the basis for that dispute. The Gibraltar government rejects Spain's argument in its entirety. They point out that as "Utrecht" ceded "the town and castle of Gibraltar, together with the port, fortifications, and forts thereunto belonging" and there were such "fortifications and forts" along the line of the current frontier (Devil's Tower, El Molino), then this area was included in the cession. Furthermore, they argue, international practice at the time was that all territorial cessions included an extended surrounding area equivalent to the length of two cannon shots. When the treaty of Seville was concluded between Great Britain, France and Spain in 1729, long arguments ensued between Spain and Britain as to how far north the 'undoubted right' of Britain extended from the north face of the Rock of Gibraltar. It was finally accepted that a distance of 600 Toises, being more than two cannon shots distance between the British guns and the Spanish guns, would be considered “the neutral ground”. In either case, the United Kingdom further bases its claim upon what they consider to be established legal precedents that grant property rights over an area that is continually occupied and made sole use of, for an extended period. In practice, the land is now an integral part of the territory of Gibraltar on one side, and similarly on the Spanish side, and, although there may be a line on the map, there is no longer any indication of the boundary of the 'neutral ground'. Maps show the evolution of the British occupation of the isthmus as well as the location of the