The proposed project aims to systematize knowledge about Aktion T-4 (i.e., Tiergarten 4 — an abbreviation derived from the address of the headquarters) carried out by the Nazis in the Wartheland territory, including in Gniezno (Gauheilanstalt Tiegenhof in Gniezno), during World War II. This operation involved the extermination of the mentally ill, whom the occupiers regarded as “an unnecessary burden” and “unproductive…