Question: Which opera was written earlier, Rienzi or Amahl and the Night Visitors? 
Sentence (from "Amahl and the Night Visitors"): It was commissioned by NBC and first performed by the NBC Opera Theatre on December 24, 1951, in New York City at NBC studio 8H in Rockefeller Center, where it was broadcast live on television from that venue as the debut production of the "Hallmark Hall of Fame".
Relevant evidence: Yes