Hector Berlioz left his home province for Paris at the age of eighteen. Obeying his physician father's wishes, he began to study medicine, although he knew he wanted to be a composer. He took up the study of composition as a private student of the then-famous Jean-François Le Sueur. Less than three years later, Berlioz's first large-scale work, a mass, was given a performance at St. Roch's church in Paris.(This work, long lost, was recently rediscovered and heard for the first time in almost 170 years.) It was only after this successful début that Berlioz, in October 1826, enrolled in the composition class at the Paris Conservatoire, where he continued to study under Le Sueur.  Simultaneously with the exercises in harmony and counterpoint required by the rigorous program, the young man had far more ambitious plans. He started working on an opera based on a libretto by his closest friend, Humbert Ferrand. The somewhat convoluted plot had a vaguely medieval flavor, reflecting the way the Romantic generation liked to think about the “dark” Middle Ages. The title Les Francs Juges referred to the members of those mysterious secret tribunals that had been introduced into recent European literature by Goethe's drama Götz von Berlichingen.

We need not dwell too long on the details of the story, replete with usurped thrones, maidens forced to marry tyrants, and man-crushing bronze statues lurking in dark caverns – especially since the opera was never performed and the score is now lost, except for the overture and a few other numbers. (One march movement, which hasn't come down to us in its original form, became the source of the “March to the Scaffold” in the Symphonie fantastique.)

Berlioz was able to obtain – not without fighting tooth and nail – the hall of the Conservatoire for an evening devoted to his works on May 26, 1828, where the overture and two excerpts were performed. The composer probably played percussion in this performance, as he did again when the overture was repeated in 1829. It was for this latter occasion that a pianissimo bass drum solo was added to the score.  (In a letter to Ferrand, Berlioz quoted one of his favorite literary works, Virgil's Aeneid, the source of his future opera Les Troyens, to describe this passage: “The great hollow space groaned and rumbled.” Virgil had said this to describe the reverberations of the Wooden Horse, struck by the Trojan spears.)
 If the opera as a whole came to nothing, the overture was a huge success, both at the first performance and later. (It became the first work by Berlioz to be performed outside France.) At the first rehearsal, it prompted enthusiastic comments from the orchestra.

The first section of the overture (“Adagio sostenuto”) opens with a soft lyrical melody that is soon followed by a striking theme played by the trombone. The fast tempo (“Allegro assai”) includes a theme coming from one of two quintets for flute and string quartet Berlioz had composed at the age of 15. Even the stern Dr. Louis Berlioz admitted that this theme had some merit. When Hector played it to him on his flute, the father said: “Ah, now that is what I call music!” 

The central part of the overture is made up of mysterious tremolos and excited accompanying figures in the strings, over which soars a new melody, played by flutes and clarinets and moving in extremely slow note-values. It was, as Berlioz later disclosed, the theme of a now-lost prayer aria from the opera. These different materials are then developed, recombined in various ways and brought to a climactic ending.

The concert of May 26, 1828, containing music from Les Francs Juges plus another overture (Waverley) and a movement from the Mass, revealed a composer who, although still officially a student, had to be taken very seriously indeed. François-Joseph Fétis, the most prominent French musicologist and critic of the day, uttered these prophetic words after the concert: “Now that is a début that will lead somewhere.”