Τ4, or "Tiergartenstraße 4," was a secret program initiated by the Nazi regime in Germany during World War II. It aimed to systematically eliminate individuals deemed "unworthy of life," including those with disabilities, mental illnesses, and other marginalized groups. The program was named after the address of its headquarters in Berlin, where the planning and execution of these atrocities took place. The T4 program involved the use of gas chambers and other methods to carry out mass killings. It is considered a precursor to the larger-scale atrocities of the Holocaust, which targeted millions of Jews, Romani people, and other groups. The T4 program was officially halted in 1941 due to public outcry, but its legacy remains a stark reminder of the dangers of dehumanization and totalitarianism.