Designed by the architect Antonio Galli Bibiena - although opposed by several others who lost the design competition - the theatre was inaugurated on 14 May 1763 with a performance of Gluck's Il trionfo di Clelia, an opera which the composer had written for the occasion. A bell-shaped auditorium consisting of four tiers of boxes plus a royal box and small gallery with a ceiling decorated as if open to the sky was built primarily of masonry as a protection against fire. However, much work remained unfinished, the facade in particular which was not completed until 1936.
Source: wikipedia.