OSWIECIM, Poland — More than 3,000 guests, including Holocaust survivors and foreign dignitaries, gathered on Tuesday at a site marking one of history’s biggest horrors, the Auschwitz-Birkenau death camps in Poland, which were liberated by Soviet troops 70 years ago in the closing months of World War II.

Because of the survivors’ advancing age, this year’s ceremony at the Auschwitz-Birkenau State Museum may be the last major anniversary celebration to include more than a handful of people who endured the Nazi camps here, where about 1.5 million people lost their lives, most of them European Jews. Some 1,500 survivors attended the 60th anniversary in 2005, but on Tuesday there were fewer than 300 on hand. Most are in their 90s, and some are older than 100.

Their dwindling numbers prompted many at the ceremony to raise the question of how best to sustain memories of the horror when they are gone, and what it means in a time of fresh outbreaks of religious and ethnic animosities.

“Today, in the name of truth, we need to fight the attempts to relativize the Shoah,” President Bronislaw Komorowski of Poland said as he opened the ceremony, using another term for the Holocaust. “The memory of Auschwitz means the memory of the importance of freedom, justice, tolerance and respect for human rights,” he added.