Original: On 29 October 1873 , the old Paris Opéra , known as the Théâtre de l'Académie Royale de Musique , which had been used since 1821 , was destroyed by a fire which raged for 27 hours , leaving the whole of Paris in despair .
Simplified: On October 29 , 1873 , the old Paris Opéra , known as the Théâtre de l'Académie Royale de Musique , which had been used since 1821 , was destroyed by a fire which burned for 27 hours .