What was the original purpose of the medium to large sized German police dog? 
Police dog:  The most commonly used breeds are the German Shepherd, Belgian Malinois and Rottweiler. Rottweiler: The Rottweiler ( or , ) is a breed of domestic dog, regarded as medium-to-large or large. Rottweiler:  The dogs were known in German as "Rottweiler Metzgerhund" , meaning Rottweil butchers' dogs, because their main use was to herd livestock and pull carts laden with butchered meat to market.
to herd livestock and pull carts laden with butchered meat to market