The New Penguin Opera Guide runs to well over 1,100 pages, and yet only four of them concern Beethoven. Of all the music the grand master wrote - some 240 works in total - he only ever composed one musical drama.
A drama, with variations, as it turned out, for the opera we know as Fidelio was 10 years in the making. There had been several false starts before it was eventually presented at the Royal Court Theatre in Vienna, on Monday May 23, 1814.
It wasn't that Beethoven wasn't interested in the form. His unsurpassed expertise in the creation of large-scale instrumental music leant itself perfectly to the theatre.
There are the overtures - Coriolanus, Egmont (part of a complete suite of music to accompany Goethe's play) - and then there's a ballet, The Creatures of Prometheus.
Circumstances, and Beethoven's legendary attention to detail - he was well-known as a perfectionist - both contributed to Fidelio's long gestation.
The opera is based on a true story from the period of the French Revolution known as the Terror. Leonore is the wife of a political prisoner. She dresses up as a boy and risks her life to get a job as a prison guard so that she can get her husband, Florestan, out of jail. Fidelio is the name she adopts in disguise.
Under the composer's preferred title, Leonore, the opera premiered in unpropitious circumstances in 1805. Napoleon's army had just occupied the city, and the opera-going public had taken to the hills. Just a few bemused French officers were in the audience. The opera bombed.
Beethoven wasn't happy with it, anyway. He took on board criticism that it was too long. He tightened up the action. Three acts became two. He wrote a new overture. He staged it again the following year.
The reception was no better. "It is impossible to understand," wrote one reviewer, "how the composer ever decided to smarten up this second-rate story with his beautiful music." It lasted just two nights.
Beethoven described Leonore as his "problem child", but he wasn't going to give up on it.
So when a revival was proposed some years later, he was prepared to give it another go, but not before there was a further extensive makeover.
The work would now be known as Fidelio. Once again, there would be a new overture, this one unlike any other. Rather than following the conventional path of presenting the various musical themes that will develop over the course of the show, the overture to Fidelio stands alone as a symphonic introduction.
The opera displays its roots in the German Singspiel tradition, where the drama is driven by dialogue as well as the music.
At the core of the story is the heroism of Leonore, unwilling to accept circumstances, driven by the love of her man to put herself in harm's way. She's out to get what's right and just, to set this prisoner free.
The struggle of light against darkness, the victory of courage against the odds, coupled with music that only Beethoven could have written made it third time lucky for Fidelio.
Its climax is a stirring chorus based on two verses from a poem by the playwright Friedrich Schiller.
Those same two verses would be heard again some 10 years later in a concert in the same Viennese Theatre, when Beethoven presented what would become his signature tune - the Symphony No 9, his 'Ode to Joy'.
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