First edition in print, edited by Conrad Gessner, of Aelianus's collected works, including On the nature of animals (On the characteristics of animals). Aelianus was a Roman author and teacher of rhetoric who flourished under Septimius Severus. Aelian's anecdotes on animals rarely depended on direct observation: they were almost entirely taken from written sources, often from Pliny, but also other authors and works now lost, for whom he is a valuable witness. Aelianus was more attentive to marine life than might be expected, and this seems to reflect personal interest; he often quotes "fishermen". At times he strikes the reader as credulous, but at others he specifically states that he is reporting what was told by others, and that he does not believe them. Aelian's work was one of the sources of medieval natural history, including medieval beastiaries 

In the 1556 edition Gessner combined the text of Claudius Aelianus with his edition of Aelianus Tacticus On military arrangements of the Greeks even though the authors and subject matters were very different. Digital facsimile of the 1556 edition from the Bayerische Staatsbibliothek at this link. English translation by A. F. Scholfield in the Loeb Classical Library (3 vols., 1958-59). Digital facsimile of the 1958-59 translation from the Internet Archive at this link.