Since [the third edition], continuing historical research and methodological changes have led to important new discoveries and to fresh interpretations of the earlier periods, necessitating a much more thorough revision. This fourth edition undertakes this. The basic outline of Walker's original text, previously modified only for the last period, has proved to be sound, and with some emendations has been generally followed again, but there has been extensive reconception, recasting, and rewriting of the content in many sections, incorporating the result of recent scholarly work in these areas
