....This is admittedly somewhat prompted by that nightmare-inducing scene of Robb Stark in Game of Thrones, but my inquiry is more general.
Was this level of mutilation and humiliation - eg. for lack of a better description, sewing bits onto other bits, followed by a parade in dubious taste - at all common? I know stories like that of William Wallace's brutal torture and execution, but it was my understanding that enemy leaders were often imprisoned, ransomed, or executed 'normally' when not killed in battle. Is it naive to assume this manner of respect for a foreign or rebellious nobleman? Or was it common to mutilate and parade about the body of a vanquished enemy?
Many thanks, and apologies for the ghoulish question.
It mostly depended on who the enemy was. A simple battle between two nations (i.e. England and France) would normally see captured knights treated honourably. As you mentioned, they would generally be ransomed and would be kept as a guest with all the respect due to them and their rank (i.e. when King John II of France was captured by the English at Poitiers, he was the guest of honour at a feast held by Edward, the Black Prince). Those who died in battle could expect a Christian burial, either on the nearest consecrated ground or potentially with their embalmed remains returned home to be buried in the local church. But again that is primarily the upper classes, those who were foot soldiers would have most likely been buried in a mass grave.
However if you were fighting someone as part of a rebellion against your lawful King, then you could expect the rather more grotesque treatments. It's reported that after Simon de Montfort was killed rebelling against King Henry III his head was cut off, and his testicles were also cut off and hung over his face. Slightly less gruesome was Richard Duke of York, the father of King Edward IV, who was decapitated after being killed in battle, and had his head mounted above the gates of the city of York with a paper crown on top, to mock his claims to the throne.
It was customary to dismember the body and send the parts to be displayed in prominent large towns, particularly in the area where a rebellion had started, in order to warn the locals of what would happen if they continued to fight their lord. But sewing bits on to other bits was not common, certainly not in England at least. Just nailing an arm to a prominent display point in the town square was considered to be enough of a deterrent.
William Wallace's crime was considered to be treason (by Edward I at least) hence the brutality of his death. King John of England, who was a particularly unpleasant character, appears to have starved a collection of French knights to death rather than let them be ransomed. But this was shocking at the time and led to further rebellions against him in Normandy.
Sources - Dan Jones' "Plantagenets" is a good read on this era. Thomas Asbridge - "The Greatest Knight" is about William Marshall and includes the early developments of chivalry, which had an impact on the treatment of prisoners of war.