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Early retirement: 1830–1855

Guillaume Tell was well received. The orchestra and singers gathered outside Rossini's house after the premiere and performed the rousing finale to the second act in his honour. The newspaper Le Globe commented that a new era of music had begun. Gaetano Donizetti remarked that the first and last acts of the opera were written by Rossini, but the middle act was written by God. The work was an undoubted success, without being a smash hit; the public took some time in getting to grips with it, and some singers found it too demanding. It nonetheless was produced abroad within months of the premiere, and there was no suspicion that it would be the composer's last opera.

Jointly with Semiramide, Guillaume Tell is Rossini's longest opera, at three hours and forty-five minutes, and the effort of composing it left him exhausted. Although within a year he was planning an operatic treatment of the Faust story, events and ill health overtook him. After the opening of Guillaume Tell the Rossinis had left Paris and were staying in Castenaso. Within a year events in Paris had Rossini hurrying back. Charles X was overthrown in a revolution in July 1830, and the new administration, headed by Louis Philippe I, announced radical cutbacks in government spending. Among the cuts was Rossini's lifetime annuity, won after hard negotiation with the previous regime. Attempting to restore the annuity was one of Rossini's reasons for returning. The other was to be with his new mistress, Olympe Pélissier. He left Colbran in Castenaso; she never returned to Paris and they never lived together again.

The reasons for Rossini's withdrawal from opera have been continually discussed during and since his lifetime. Some have supposed that aged thirty-seven and in variable health, having negotiated a sizeable annuity from the French government, and having written thirty-nine operas, he simply planned to retire and kept to that plan. In a 1934 study of the composer, the critic Francis Toye coined the phrase "The Great Renunciation", and called Rossini's retirement a "phenomenon unique in the history of music and difficult to parallel in the whole history of art":

Is there any other artist who thus deliberately, in the very prime of life, renounced that form of artistic production which had made him famous throughout the civilized world?

The poet Heine compared Rossini's retirement with Shakespeare 's withdrawal from writing: two geniuses recognising when they had accomplished the unsurpassable and not seeking to follow it. Others, then and later, suggested that Rossini had retired because of pique at the successes of Giacomo Meyerbeer and Fromental Halévy in the genre of grand opéra. Modern Rossini scholarship has generally discounted such theories, maintaining that Rossini had no intention of renouncing operatic composition, and that circumstances rather than personal choice made Guillaume Tell his last opera. Gossett and Richard Osborne suggest that illness may have been a major factor in Rossini's retirement. From about this time, Rossini had intermittent bad health, both physical and mental. He had contracted gonorrhoea in earlier years, which later led to painful side-effects, from urethritis to arthritis; he suffered from bouts of debilitating depression, which commentators have linked to several possible causes: cyclothymia, or bipolar disorder, or reaction to his mother's death.

For the next twenty-five years following Guillaume Tell Rossini composed little, although Gossett comments that his comparatively few compositions from the 1830s and 1840s show no falling off in musical inspiration. They include the Soirées musicales (1830–1835: a set of twelve songs for solo or duet voices and piano) and his Stabat Mater (begun in 1831 and completed in 1841). After winning his fight with the government over his annuity in 1835 Rossini left Paris and settled in Bologna. His return to Paris in 1843 for medical treatment by Jean Civiale sparked hopes that he might produce a new grand opera – it was rumoured that Eugène Scribe was preparing a libretto for him about Joan of Arc. The Opéra was moved to present a French version of Otello in 1844 which also included material from some of the composer's earlier operas. It is unclear to what extent – if at all – Rossini was involved with this production, which was in the event poorly received. More controversial was the pasticcio opera of Robert Bruce (1846), in which Rossini, by then returned to Bologna, closely cooperated by selecting music from his past operas which had not yet been performed in Paris, notably La donna del lago. The Opéra sought to present Robert as a new Rossini opera. But although Othello could at least claim to be genuine, canonic Rossini, the historian Mark Everist notes that detractors argued that Robert was simply "fake goods, and from a bygone era at that"; he cites Théophile Gautier regretting that "the lack of unity could have been masked by a superior performance; unfortunately the tradition of Rossini's music was lost at the Opéra a long time ago."

The period after 1835 saw Rossini's formal separation from his wife, who remained at Castenaso (1837), and the death of his father at the age of eighty (1839). In 1845 Colbran became seriously ill, and in September Rossini travelled to visit her; a month later she died. The following year Rossini and Pélissier were married in Bologna. The events of the Year of Revolution in 1848 led Rossini to move away from the Bologna area, where he felt threatened by insurrection, and to make Florence his base, which it remained until 1855.

By the early 1850s Rossini's mental and physical health had deteriorated to the point where his wife and friends feared for his sanity or his life. By the middle of the decade, it was clear that he needed to return to Paris for the most advanced medical care then available. In April 1855 the Rossinis set off for their final journey from Italy to France. Rossini returned to Paris aged sixty-three and made it his home for the rest of his life.