We are grateful to the Master and Fellow of St John's College, Cambridge, for funding of the December 2001 conference on which this volume is based; and to all who participated in that event. We would also like to thank Michael Sharp and Sarah Parker at Cambridge University Press, and the anonymous readers for the volume; and also colleagues at Cambridge, Exeter and St Andrews, many of them working on related projects, for ideas and support (within the Exeter Centre for Hellenistic and Romano-Greek Studies and the St Andrews Logos Centre for study of ancient systems of knowledge). We are grateful especially to Simon Goldhill for comments on Chapter 1.