If you are talking about Anglo-American law, you can make a far better argument that they arenu2019t. Real property law derived from Domesday Book after the Norman Conquest in 1066 CE. Greater scholars, like Plucknett and Vinogradoff back to Maitland have traced it back to Roman roots in dominium. The key policy thread was clarity of title as the basis for consistent u201ctaxation.u201dContract law begins to evolve much much later in the writ of assumpsit. Arguably, it evolved from the earlier writs regarding enforceable rights derived from possession, like debt and case. A respectable argument can be made to contradict that conclusion, but the date is in the 14th century.It has been argued, first by Ms. Shapiro, that loan enforcement law and possessory law both arise at the time of Richard Coeur du2019Lion as a means of financing the Crusades with loans from the London Jewish community. Professor Broyde published a brief article suggesting that bailment also comes to us from the Talmud. And, I believe I have demonstrated in my article published in The Conveyancer in London that most of commercial law draws its principles from Talmud and cannot be traced to the Romans, Greeks, or others, as casually asserted without citation by Professor Jolowicz. A complete version of the article with all footnotes and citations is on my office web site here. http://sternberglaw.net/wp-conte... That influence ended with the Edwardian expulsion of the Jews in 1290 CE, not long but distinctly before the advent of assumpsit. The mortgage was an invention modifying Jewish law of contracts to permit enforcement against English estates without giving the creditor the ability to take title. Soon thereafter, English law invented enforcement of assumed obligations including contracts.So, plainly, the later enforceable contract arising from a voluntarily assumed duty could not have been the historic source for property rights that were of ancient Roman or at least Norman origin or for commercial rights that existed years before.