 Some scholars believe that constitutional norms do not exist unless they are in some way enshrined in a written document (e.g., Rubenfeld 1998). But most accept that constitutions (or elements of them) can be unwritten, and cite, as an obvious example of this possibility, the constitution of the United Kingdom. One must be careful here, however. Though the UK has nothing resembling the American Constitution and its Bill of Rights, it nevertheless contains a number of written instruments which have, for many centuries, formed central elements of its constitution. Magna Carta (1215 C.E.) is perhaps the earliest document of the British constitution, while others include The Petition of Right (1628) and the Bill of Rights (1689). Furthermore, constitutional limits are also said to be found in certain principles of the common law, explicitly cited in landmark cases concerning the limits of government power. The fact remains, however, that historically the constitution of the UK has largely taken unwritten form, suggesting strongly that writtenness is not a defining feature of constitutionalism.