The Laudes Regiæ (English: Royal Praises or Royal Acclamations) is a hymn used in the rites of the Catholic Church. There are variant texts, but they most often begin with these words that give the hymn its alternative title: Christus vincit! Christus regnat! Christus imperat! (English: Christ conquers, Christ reigns, Christ commands). . The melody of the refrain is used as an interval signal for Vatican Radio's shortwave transmissions. History.
https://en.wikipedia.org/wiki/Laudes_Regiae