Several of the chapters in these volumes are appearing in print for the first time. But most of them have been published before (although generally in a very different form) either as articles in journals or as contributions to collective works. Revising them for re-publication, I have attempted to tread two slightly divergent paths at the same time. On the one hand, I have mostly allowed my original contentions and conclusions to stand without significant change. Where I no longer entirely endorse what I originally wrote, I usually indicate my dissent by adding an explanatory footnote rather than by altering the text. I have assumed that, if these essays are worth re-issuing, this can only be because they continue to be discussed in the scholarly literature. But if that is so, then one ought not to start moving the targets.

On the other hand, I have not hesitated to improve the presentation of my arguments wherever possible. I have corrected numerous mistranscriptions and factual mistakes. I have overhauled as well as standardised my system of references. I have inserted additional illustrations to strengthen and extend a number of specific points. I have updated my discussions of the secondary literature, removing allusions to yesterday's controversies and relating my conclusions to the latest research. I have tried to make use of the most up-to-date editions, with the result that in many cases I have changed the editions I previously used.