Legal: The Statute of Treasons of 1351

One of the worst offenses imaginable in Medieval life was treason against the king, or against one's overlord in the feudal system.  Under English common law, this crime could encompass doing almost anything the King or Lord didn't like from outright rebellion to poaching or stealing.  For this reason, the Parliament under Edward III in 1351 saw fit to codify exactly what was and wasn't treason.

They classified two levels of treason.  High treason was offenses against the King, including encompassing (planning or imagining) the death of the King or his son and heir, sexual relations with a companion (mistress of the King), though not necessarily his wife, though seducing the King's unmarried eldest daughter or the wife of his son was also treason.  Waging war against the King in his realm or aiding his enemies, counterfeiting the Great Seal or the royal coinage, or killing one of the King's Great Officers, such as the Chancellor, the Treasurer or the like was also treason.  The law also defined petty (petit) treason, such as the murder of one's lawful superior, an underling killing his lord, or a wife her husband.  The law also contained a catch-all provision for future offenses which the monarch could deem treasonous, such as heresy.  Portions of this law are still in effect today.