Piero Terracina was 15 years old in 1944 when two SS soldiers entered the home in Rome where he and his parents, his grandfather, his two brothers and sister and an uncle had gathered to celebrate Passover. They were deported to Auschwitz, the Nazi death camp in Poland, where only Mr. Terracina emerged alive.

After maintaining a long silence about his experience in the camp — an existence that he compared to a double life, as he went about his normal activities by day and endured nightmares of Auschwitz by night — Mr. Terracina found purpose and meaning as one of Italy’s most prominent witnesses to the Holocaust.

For years he devoted himself to the cause of memory-keeping, speaking to public officials, to historians and journalists and especially to students, often accompanying them on trips to Auschwitz. His presence became only more powerful and more poignant with the passage of time.

Mr. Terracina, one of the last remaining Italian survivors of the Holocaust, died Dec. 8 at a hospital in Rome. He was 91. His death was confirmed by Daniel Funaro, an official of the city’s Jewish community, who did not cite a specific cause.

Liliana Segre, a fellow Italian survivor and senator-for-life who recently made international news when she was placed under police protection because of anti-Semitic threats, told Italian media after Mr. Terracina’s death that his loss made her feel “ever more alone.”

Piero Terracina, the youngest of four children, was born in Rome on Nov. 12, 1928, to a religious family that belonged to the city’s ancient Jewish community. His father was a fabric merchant.

In an oral history with interviewer Luigi Di Palma, he emphasized that his personal Holocaust “hell” did not begin with his deportation by the Nazis in 1944, but rather six years earlier, with the promulgation of Italy’s anti-Semitic racial laws under the fascist dictatorship of Benito Mussolini in 1938.

Around his 10th birthday, he and other Jewish children were expelled from public schools. “The teacher whom I loved and who loved me told me not to enter,” he said in remarks published in the Italian newspaper the Corriere della Sera. “Terracina,” he recalled her saying, “you stay outside.”

For a boy raised to enjoy and value his studies, his expulsion was wrenchingly painful. He enrolled at a Jewish school and carried on, even as the racial laws made daily life ever more difficult for Italian Jews.

Their fortunes changed dramatically for the worse on Sept. 8, 1943, when Italy, which had previously sided with the Axis powers, surrendered to the Allies. The Germans occupied the northern and central parts of the country and commenced roundups of Jews.

Mr. Terracina and his family survived the most infamous of them, which took place on Oct. 16, 1943, when the Nazis descended on Rome’s old ghetto and arrested more than 1,000 Jews for deportation.

The family obtained false identity cards and lived for a period in hiding, according to a testimony he provided to the Center for Contemporary Jewish Documentation in Milan. On April 7, 1944, they had convened for their Passover celebration when two Italian informants, financially compensated for the deed, accompanied the SS soldiers to their door.

As Mr. Terracina wept, his father implored him: Whatever happens, do not abandon your dignity. Decades later, Mr. Terracina would sometimes weep again when he conveyed those words to the students to whom he offered his testimony.

The family was first incarcerated at the Regina Coeli prison in Rome, then at the Fossoli internment camp near Modena, before they were loaded onto trains to Auschwitz. Quickly separated from his mother and father, he asked another inmate where his parents had gone.

“Do you see the smoke?” the inmate said, referring to the chimney of the crematorium.

Mr. Terracina was subjected to forced labor and weighed little more than 80 pounds when Auschwitz was liberated by Soviet troops on Jan. 27, 1945.

Just as they were arriving, Mr. Terracina told the University of Southern California Shoah Foundation, he had stepped outside his barrack to collect snow to melt into water to quench his thirst.

“I saw a man in front of me, a young man all dressed in white. He was wearing a white cape or a sheet to camouflage himself in the white snow,” Mr. Terracina said. “I went back inside the barrack and immediately told my companions, ‘They have arrived.’ ”

“There were no scenes of enthusiasm or jubilation,” he continued. “I remember total silence.”

He made his way home to Italy, with a detour through the Soviet Union and Eastern Europe, and was reunited with several cousins and friends from his Jewish school to whom he credited his life after the war. Mr. Terracina made a living in business and had no immediate survivors.

He told the Union of Italian Jewish Communities that he did not speak about the war because he feared questions about how he survived. He could not bear the thought, he said, of having to explain why he lived and someone else’s husband or son did not. He said he also worried that people would not believe him, and that revisiting his memories would pull him into the past and out of the present, where he sought a normal life.

In time, he became persuaded of the importance of offering his testimony, which he gave to thousands of students in the later years of his life. He drew a distinction between recollection, which he said dies with the person who carries it, and memory, which he compared to a thread linking the past and future.

One student was so moved by his story that he or she left him an anonymous note asking for forgiveness for the actions of a fascist grandfather.

“I would like to respond with these words,” Mr. Terracina said in public remarks reported by the Italian news agency ANSA. “Don’t worry, young man or young woman. Your grandfather’s actions are a lesson for you, but grandchildren do not bear the guilt for what their grandparents have done, just as children do not bear the guilt for what their parents have done. What matters is that you recognize and understand the lesson, what is right and what is wrong.”