  A key figure in the emergence of this new type of sophist was Protagoras of Abdera, a subject city of the Athenian empire on the north coast of the Aegean. Abdera was also the birthplace of Democritus, whom some later sources represented as the teacher of Protagoras. In all probability Democritus was the younger of the two by about thirty years, and the only solid evidence of intellectual relations between them is a statement by Plutarch (Against Colotes. 1108F) that Democritus argued against Protagorean subjectivism (see below), complemented by Sextus, who reports (Against the Mathematicians VII.389–90) that Democritus’ arguments included the argument that Protagoras’ subjectivism is self-refuting. Protagoras was one of the earliest sophists; as presented in Plato’s Protagoras (one of our principal sources for Protagoras’ life and activities as a teacher) he says (317c) that he is old enough to be the father of anyone present, who included rival sophists Hippias and Prodicus, while another Plato passage (Meno 91e) says that he practised as a sophist for over forty years till his death at about seventy (probably about 420 BC). In the Protagoras he also says (316d–317b) that while the activity of sophistry has been practised by poets and other experts from ancient times, he is the first person to have openly proclaimed himself a “sophist” and claimed to teach people (sc. how to achieve success in life); he thus claims for himself recognition of his professional status in a role, that of teacher of human excellence as a means to success in life, which was traditionally claimed by the poets