In one of the funnier scenes from Monty Python and the Holy Grail, peasants approach a knight. they have accused a local woman of being a witch and demanding justice.
Suffice to say that to test whether or not she is indeed a witch, the knight rules that she must be thrown into the water. If she floats; she is then guilty of being a witch.
As funny as this bit of theater is, it is actually based loosely on European and, therefore, Crusader law. Our ancestor, Usama ibn Munqidh recorded a similar scene in his autobiography Kitab al-I’tibar (Arabic: كتاب الاعتبار, The Book of Learning by Example).
Usama was a Syrian knight/warrior, poet, diplomat, soldier, hunter, and nobleman of the 12th century and lived during the Crusades.
He recounts an example of crusader law in which a local man was accused of attacking, robbing, and killing Christian pilgrims. The man was caught and was put on trial in the local court (assize). Such courts were presided over sometimes by a local lord or viscount. In other instances, several local crusader knights would preside.
The crusader court in accordance with their law decided the accused would undergo trial by water. He was tied up and thrown into a cask of water. As Usāma explained, if he were innocent, he would sink, and if guilty, he would float. The man tried to make himself sink, but he could not. Thus he was pronounced guilty and was blinded as his punishment. He did not get better.