A hatred of tyranny and oppression had been instilled in Dallapiccola from an early age. He was born on February 3 1904, in a frontier town on the Istrian peninsula near Trieste. At the time it was part of the Austro-Hungarian Empire, though after the first world war it reverted to Italy. (It is now in Croatia.) The composer recalled that when a train pulled in to the local station, the guard would announce its name in three languages: Mitterburg/Pisino/Pazin - an indication of its status as a cultural melting-pot. The Austrian authorities were quick to stamp on any suspected irredentist sympathies among the Italian population, and Dallapiccola's father - a classics teacher at the only Italian-language school - was considered "politically unreliable". As a result the school was closed down, and the family deported to the Styrian capital of Graz.  

The experience of internment left a deep scar on Dallapiccola. The Canti di Prigionia (scored for chorus with an instrumental ensemble consisting of two harps, two pianos and percussion) sets texts by three condemned prisoners: Mary Stuart, Boethius and Savonarola. Mary Stuart's fervent prayer for freedom struck a particularly strong chord: "I wanted," Dallapiccola said, "the divine word libera to be shouted by everyone." Some five years later, when his only child was born shortly after the libera tion of Florence from the Nazi occupation in August 1944, she was named Annalibera.  

Dallapiccola's progress towards 12-note music was a gradual one, and it was made difficult by the lack of performances of the music of Schoenberg, Berg and Webern in Italy. But he managed to acquire a score of Berg's Wozzeck and, in 1934, he heard the same composer's concert-aria Der Wein at a contemporary music festival in Venice. The two works left an indelible impression on him - as did Lulu, of which he heard the first broadcast performance in 1937. At that time Dallapiccola was working on his own first opera, Volo di Notte (based on Saint-Exupéry's novel Vol de Nuit), and Berg's influence can be heard throughout: in the opera's symphonic musical forms; in the casting of one of its scenes as a "pezzo ritmico" (an idea that harks back to the "monoritmica" that reaches its climax with the suicide of Lulu's husband in the first act of Berg's opera) and in the Movimento di Blues, which echoes the off-stage jazz band interludes that punctuate the scene in Lulu's dressing-room.

Dallapiccola lived in Florence for more than 50 years, the majority of them in an apartment in the Via Romana overlooking the Boboli Gardens, and his exquisitely executed scores have an air of Florentine craftsmanship about them. Even the look of the music on the page carries symbolic significance, as it occasionally does in Italian renaissance music. In his one-act opera Il Prigioniero, set during the Spanish Inquisition, a prisoner is led to believe that freedom is at hand. He manages to escape his cell but as he emerges into a starlit garden, only to fall into the arms of the Grand Inquisitor, he understands that all the events leading to his escape have been pre-arranged as the ultimate torture - hope. In the music, a complex web of ricercars, or intricate contrapuntal studies, seems to reflect the labyrinth of Saragossa's subterranean corridors through which the prisoner stumbles.

In the beautiful late piece Sicut Umbra ... for mezzo-soprano and chamber ensemble, Juan Ramón Jiménez's lines "Hay que buscar, para saber tu tumba, por el firmamiento" ("You have to search the firmament to know your tomb") are mirrored by melodic lines based on the shapes of various constellations, which Dallapiccola "draws" in the score. And the Cinque Canti of 1956 for baritone and chamber ensemble use a 12-note row whose sinuous line suggests the shape of a crucifix. At the work's mid-point a single "tutti" chord in an otherwise sparsely scored passage enables Dallapiccola to "draw" an actual cross on the page. The listener may not consciously be aware of such symbolic devices, but they nevertheless cast a metaphysical shadow over the music.  

At the heart of Dallapiccola's art lie elaborate canons of every conceivable kind. They are heard at their most serenely simple in the Wartime Series of Greek Lyrics the composer wrote as a mental refuge from the turmoil that surrounded him. More complex are the Goethe-Lieder of 1953 for voice and three clarinets, based on poems from the Westöstlicher Divan. In one, the character of Suleika contemplates her reflection: "The mirror tells me I am beautiful. You tell me it is also my fate to age." Dallapiccola writes a mirror-canon, with the answering voice not only upside-down but also in a refracted rhythm that suggests the process of ageing, as though in a distorted looking-glass.  

There is in Dallapiccola's art a touching faith in the 12-note system, almost as a way of life. That faith is one that is deeply unfashionable today. Thirty years ago, at the time of the composer's 70th birthday, I produced a retrospective evening of his work for Radio 3, and I remember asking him what was being done in Italy to mark the occasion. "I think nothing," he said, with a resigned shrug of the shoulders.  

At least this time round, on his centenary, there will be performances of his music in Rome and Florence. But over here there have been precious few attempts to spark a revival of interest in recent years, other than a rather ill-judged production of Il Prigioniero at English National Opera. It's difficult to know why this hauntingly beautiful music remains so little known to all but a small circle of admirers. Certainly, it is undemonstrative in its perfection; but that very perfection is a quality we should treasure.