Johannes Lydos quotes a passage from a lost military work on warfare against the Parthers in De magistratibus 3, 34. The author of this work, which dates from 63 AD, is said to be Κέλσος ὁ Ῥωμαῖος τακτικός, who has repeatedly been identified as Marius Celsus in several research studies. This article, however, depicts the encyclopedist and medical practitioner Aulus Cornelius Celsus as the author of this military writing. It first provides a retrospective of the research done. Secondly it shows (...) that two military writings are likely to exist in the works of Celsus and in a third step it puts forward a decisive argument against Marius Celsus. Finally, some further reflections on his interests and lifetime hint at Aulus Cornelius Celsus being the author. (shrink)