Descended from Roman drover dogs, the Rottweiler (the ninth most popular dog in the U.S. in 2015) likes to move. According to the AKC, Rotties should be exercised at least twice a day. Though the powerful dog can be reserved with strangers, it is also considered an affectionate pet and devoted companion. Even so, because of their muscular build and size — 24 to 27 inches (60 to 69 centimeters) at the shoulder, and weighing 95 to 125 pounds (43 to 57 kilograms) — owners must be careful having Rottweilers around small children, according to the American Rottweiler Club. Apparently, the dog’s “bumping” behaviors can knock kids over: “This bumping is a natural behavior of the Rottweiler, a legacy from the days when the breed was used to herd cattle. Rottweilers will bump and herd children or elderly family members