16. Saint Bernard
Saint Bernards are among the world’s most popular breeds. Native to the Swiss Alps, these enormous dogs are famous for their mountain rescue missions in freezing temperatures. Females typically weigh 120–140 pounds, while males range from 140–180 pounds, and they may not realize their own strength. Though usually gentle and smart, they can become aggressive if not properly socialized. What children find amusing can quickly turn dangerous, making training necessary for this and many other breeds.