The Spanish claim makes a distinction between the isthmus that connects the Rock to the Spanish mainland on the one hand, and the Rock and city of Gibraltar on the other. While the Rock and city were ceded by the Treaty of Utrecht, Spain asserts that the "occupation of the isthmus is illegal and against the principles of International Law". The United Kingdom relies on ''de facto'' arguments of possession by prescription in relation to the isthmus, as there has been "continuous possession of the isthmus over a long period".