Historians are not sure when humans first started keeping animals as pets. Keeping an animal for pleasure rather than for food or work was possible only for people who were well off and had the resources to feed extra mouths. Dogs most likely were the first pets, because they were domesticated so long ago. The ancient Romans are known to have kept pets, particularly dogs and birds. Cats and horses were also popular with Romans and may have been considered pets, but they were also working animals. The origins of ornamental goldfish date back to the seventh century in China, where Buddhist monks first raised them in ponds. By the fourteenth century the Chinese were keeping goldfish indoors in bowls as pets.