Gorgias' visit and the rhetorical exhibition he displayed before the Athenians is traditionally considered as coinciding with the apparition of rhetoric as a wide-spread discipline at Athens.
Bouchard, Elsa. "Gorgias' visit to Athens". The Literary Encyclopedia. First published 01 March 2010
[http://www.litencyc.com/php/stopics.php?rec=true&UID=11229, accessed 24 May 2013.]