burial chamber vs catacomb

burial chamber

noun
  • A chamber, often below ground level, used to bury the remains of the dead. 

catacomb

noun
  • An underground system of tunnels and chambers with recesses for graves, used (in former times) as a cemetery; a tunnel system used for burying the dead, as in Paris or Ancient Rome. 

How often have the words burial chamber and catacomb occurred in a corpus of books? (source: Google Ngram Viewer )