No law of the Kingdom of Jerusalem and few incidents in its constitutional history have received so much attention from recent historians as the Assise sur la ligece and the establishment of the Commune of Acre. But perhaps for the reason that a great achievement of the last few years has been the delineation of the twelfth-century monarchy, the later history of the Assise and its practical application in a series of disputes between the government and the baronage have not received much attention. The sources for the Assise all date from the middle years of the thirteenth century, by which time the Palestinian jurists' interpretation of it was at the end of a long period of development; and there is something to be said for trying to trace its history from that moment towards the end of the twelfth century when it became the basis for baronial resistance to the crown. In this paper, therefore, I will study the law's development from the reign of Aimery (1198-1205). I will argue that it was in the course of a dispute between that king and Ralph of Tiberias that the Assise was interpreted in such a way as to justify open opposition to arbitrary acts by the king; that this interpretation was used with most success early in 1229, during the Crusade of the Emperor Frederick II; but that, as far as the Kingdom of Jerusalem was concerned, the creation of the Commune of Acre in 1231-2 coincided with its final failure, and events at that time revealed inherent weaknesses in its use as an instrument of resistance. It follows that the detailed treatment of the law by Philip of Novara and John of Jaffa some decades later is a further demonstration of their fascinating but essentially unrealistic vision.