‘Men dred tresson wher they it finden’ wrote an anonymous fifteenth-century translator of the Song of Roland, the earliest and greatest of all chansons de geste which take treason as their major theme. In later medieval France men did not have far to search before they found evidence justifying concern with that particular topos. Treason was often associated with its sister sedition in contemporary chronicles, memoirs, pamphlets, sermons and political allegories, even in figurative representations of that betrayal, most notorious to medieval men, by Judas of his Lord. The long war with England naturally posed delicate problems over the loyalty and allegiance of many involved in conflict through no choice of their own. Aspects of what happened when individuals changed sides and whole provinces bent before force majeure in recognizing a new sovereign, thereby incurring the stigma of rebellion against a former lord, have recently been much discussed. Plots to deliver castles and towns are without number. Siege warfare, so characteristic of the period, encouraged such behaviour. Surviving interrogations reveal both serious and improbable schemes to over-throw royal authority, in which great provincial princes were often implicated. Thousands of letters of pardon recite, frequently in the graphic words of the guilty, the extent of innumerable individual acts of treachery towards the French crown. The use of spies and informers, coded and cryptic messages, poisoning, assassination, torture, bribery and blackmail, pre-arranged meetings with mysterious figures and also the invocation of intangible occult forces, sorcery, divination and black magic, to attain political ends, all these are integral to the most notorious cases of treachery.