The Holy Roman Empire was founded in 962 when Otto the Great, King of Germany and Italy or Lombardy was crowned Emperor. All Emperors since then were kings of Germany and Italy, and since 1032 kings of Arles or Burgundy also.
But I read that it was illegal for there to be any kingdoms (except for Bohemia) in the Holy Roman Empire.
However, according to Germanic law at that time, no kingdoms could exist within the Holy Roman Empire, with the exception of the Kingdom of Bohemia.
Does anyone know if there actually was such a law?