Complex sentence: Sumner notes that death by burning for heretics was made positive law by Pedro II of Aragon in 1197, in 1224 Frederick II, Holy Roman Emperor, made burning a legal alternative, and in 1238, it became the principal punishment in the Empire.
Split into simpler sentences: Sumner notes that death by burning for heretics was made positive law by Pedro II of Aragon in 1197. In 1224 Frederick II, Holy Roman Emperor, made burning a legal alternative, and in 1238, it became the principal punishment in the Empire.