The street name probably comes from the old German Raas (moat, watercourse). In 1382 it was called "Antiquum raes" to distinguish it from the "Novum raes" (both Kleine Hosennähergasse und Große Hosennähergasse). In modern times, nobody knew the word Raas anymore, so people spoke of Ross, albeit it means horse, but also the same as "Idiot" in Bavaria. After the war it was called ul. Rumacza = Rosstraße for a short time. The current name means swampy alley.