Musicologists now believe that because Vivaldi was still a priest he may not have wanted to attract attention to an activity possibly seen as frivolous. The theatre's directors were Vivaldi and his musician father, but the fact that this opera was by Vivaldi himself went unnoticed by posterity.

In 1714, an Orlando opera was a huge hit at the Teatro San Angelo in Venice, running for 40 performances – a long run at the time. It's very exciting.' Although the manuscript was among vast numbers of Vivaldi papers in an Italian library, it had been overlooked because it did not bear a composer's name. Federico Maria Sardelli, the Vivaldi scholar who initially identified the master's hand, said: 'The music is completely new for everybody. 'It's a gift from heaven,' said Susan Orlando, a Vivaldi expert.

It contains as many as 20 new arias, never heard before – all composed around the time that Vivaldi was also working on The Four Seasons, said to be the most-recorded piece of classical music in history. The manuscript has been dated to 1714, 13 years before Vivaldi composed his later masterpiece.

Vivaldi operas naive