ROME (AP) — Giulietta Simionato, an Italian mezzo-soprano whose instantly recognizable voice was wildly popular with audiences, died Wednesday, La Scala opera house said. She would have turned 100 on May 12.

Simionato, a great friend of Maria Callas and the president of the Maria Callas Association, died at her home in Rome, the ANSA news agency reported, citing the director Bruno Tosi.

Simionato landed an audition at La Scala in 1933, after winning a singing competition in Florence.

Her voice though wasn't judged mature enough, so she only had secondary roles until 1947, when she was given the title role in Thomas' "Mignon." Over a 30-year career at La Scala, she sang Amneris, Eboli, Azucena, Rosina, Cenerentola, Tancredi, Cherubino, Donna Elvira, Orfeo, Ifigenia and Carmen, the opera house said.

Her American debut was at the Lyric Opera of Chicago in the company's debut season in 1954.

In a tribute to the Lyric to mark its 50th anniversary, Simionato recalled one of her subsequent performances in Chicago when she fell onstage during a performance of Cilea's "Adriana Lecouvreur." She was whisked up to the opera's first aid station and a plaster cast put on her leg.

"In such a state with heavy doses of medications to ease the intense pain I nevertheless felt able to undertake Act Three, but there was a problem: I absolutely could not move a step," she recalled in the tribute. "Meanwhile the public was becoming increasingly nervous and apprehensive, until it exploded in a deafening applause of relief ... at the moment when I finally reappeared onstage in costume and with my plaster cast, gently positioned in a wheelchair improvised for the occasion and escorted by two lackeys dressed up in wigs and costumes (we were, after all, still in the eighteenth century!!)."

She made Metropolitan Opera debut on opening night of the 1959-60 season as Azucena in Verdi's "Il Trovatore," in a new production that included Carlo Bergonzi, Antonietta Stella and Leonard Warren.

Winthrop Sargeant wrote in The New Yorker that she "sang the role of Azucena with a degree of authority, power, and musical taste that I have not heard approached in this part since the days of the great Bruna Castagna." He went on to describe her as "a small, round-faced woman with an intense stage personality that matches her extraordinary vocal gifts."

She sang with the Met just 28 times, including tour performances, also appearing as Santuzza in Mascagni's "Cavalleria Rusticana," Amneris in Verdi's "Aida," Rosina in Rossini's "Il Barbiere di Siviglia," Dalila in Saint-Saens' "Samson et Dalila" (singing in Italian while the rest of the cast sang French). Her last performance at the Met was in 1962, but she did go on a U.S. tour with the company in 1965.

She officially retired in 1966 singing in Mozart's "La Clemenza di Tito" in La Piccola Scala.

In its tribute, La Scala praised her "expansive, balanced, emotional and recognizable" voice as well as her personal character.

"Few 'family artists' have been so loved, and no book on the history of opera can consider itself complete without a chapter on her dazzling career," La Scala said.

Simionato and Callas sang a historic duet in 1957 in Donizetti's "Anna Bolena."

Funeral services were scheduled for Thursday in Rome, ANSA said.