Animals had a variety of roles and functions in ancient Greece and Rome. Fish and birds were served as food. Species such as donkeys and horses served as work animals. The military used elephants. It was common to keep animals such as parrots, cats, or dogs as pets. Many animals held important places in the Graeco-Roman religion or culture. For example, owls symbolized wisdom and were associated with Athena. Humans would form close relationships with their animals in antiquity. Philosophers often debated about the nature of animals and humans. Many believed that the fundamental difference was that humans were capable of reason while animals were not. Philosophers such as Porphyry advocated for veganism.