Aesop's Fables is a collection of fables credited to Aesop, a slave and story-teller believed to have lived in ancient Greece between 620 and 560 BCE. Of diverse origins, the stories associated with Aesop's name have descended to modern times through a number of sources. They continue to be reinterpreted in different verbal registers and in popular as well as artistic mediums. In Classical times there were various theorists who tried to differentiate these fables from other kinds of narration. They had to be short and unaffected; in addition, they are fictitious, useful to life and true to nature. In them could be found talking animals and plants, although humans interacting only with humans figure in a few.