Each concentration camp prisoner was assigned a number, known as their prisoner number, when they arrived at a camp. In the concentration camps, these numbers were more important than the prisoners’ names. During roll call, for example, prisoners had to report with their number instead of their given name. Sometimes the same number was assigned multiple times in the camps – after large numbers of prisoners had been released or transferred, for example, or when prisoners died. Furthermore, prisoners almost always received a new number when they were transferred to a different camp. In some cases, multiple people were assigned the same prisoner number at different times. Nonetheless, the prisoner number is often the most precise way to identify a person. On some concentration camp documents, the prisoner number was used in place of the person’s name. For this reason, ITS employees also wrote the prisoner number on the envelopes to clearly attribute the documents to the individual.