The tattoo that Wiesel receives is given to him by the Nazi soldiers. From that point on, Elie is not referred to by his name, but rather by his number. This is another example of the dehumanization of the Jewish people by their Nazi captors. First, the Nazis take the Jewish people's homes, then they take their families (when they separate them just off the trains), then they take their clothes, and finally, they take their identities, by using the same type of number identification system that is used with cattle. In the end, the Nazis will take many Jewish lives as well, including those of members of Elie's family.
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According to the Holocaust Encyclopedia, tattoos were only issued at Auschwitz concentration camp complex. In Chapter 3 of Night, Elie and his family are brought to Auschwitz-Birkenau where they are given tattoos of numbers on their arms. Elie's number is A-7713. The SS authorities used tattooing primarily as a means of identification. After the Jews in the camp died, their clothing was removed, and this tattooed number was the only means of identifying the bodies. However, those who were sent to the gas chambers immediately were not tattooed. Inmates also had to show their numbers at different times—one of which was in order to receive food.
As he moves in one line to be tattooed, Elie finds himself face-to-face with the notorious "Angel of Death," Dr. Mengele. After Elie and his father are marked with numbers, they are moved to another place that has no floor. There they wait and spend their time sleeping. Some of the prisoners have been sent to the gas chambers, but Elie and his father are among those who are marched for four hours to Buna three weeks later.
Elie comments on this time in his life:
I thought of us as damned souls wandering through the void, souls condemned to wander through space until the end of time, seeking redemption, seeking oblivion, without any hope of finding either. (Ch.3)
His despair is in sharp contrast to the giggling German girls who allow the Nazi guards taking the Jews to Buna to flirt with them and even kiss them.