mayor of the palace vs prefect

mayor of the palace

noun
  • In the Merovingian kingdoms, the king’s steward and, by the 7th century, de facto regent. 

prefect

noun
  • An official of Ancient Rome who controlled or superintended a particular command, charge, department, etc. 

  • The head of a department in France. 

  • A school pupil in a position of power over other pupils. 

  • A commander. 

  • The head of a county in Albania or Romania. 

  • The head of a prefecture in Japan. 

How often have the words mayor of the palace and prefect occurred in a corpus of books? (source: Google Ngram Viewer )