As an undergraduate studying history, my interests had often tended towards the relationship between armies and politics. When it came to modern history, military dictatorships in Africa and Latin America were a source of fascination, and as a fledgling ancient historian, I was drawn to the Barcids and the Diadokhoi, generals who had achieved political supremacy over the states they served on the battlefield. As I came to the end of my Honours year at the University of Sydney, I assumed that the third century BC would continue to be the temporal realm of my research. However, when my PhD supervisor, Professor Richard Miles, suggested that I study the Tetrarchs, my trajectory suddenly changed direction towards the other third century. Given my fascination with military politics, the third century AD proved irresistible to me, and it is thanks to Professor Miles’s prescience that I have found such intellectual stimulation and enjoyment in the study of the Tetrarchs and in the regimes that came before and after their rule. I can only hope that readers will find similar stimulation and enjoyment in reading the work that I have produced.

This book began as my PhD dissertation, which I completed at the University of Sydney in 2018. It is a book about dynastic and military politics in the Tetrarchic period, and as such it tackles a notoriously contentious topic. Why did the imperial succession in AD 305 happen the way it did? Was Constantine an heir apparent? These and related questions have produced diverse responses and passionate disagreements. While I seek to be persuasive, I look forward to the discussions that I hope this book will elicit.

Many have helped me along the way in producing this monograph. At the outset I would like to thank Professor Miles. Despite my penchant for detail, he directed me to keep my eyes on the bigger questions. I also offer deeply felt thanks to the following scholars who, through their suggestions, criticisms and/or proofreading, greatly helped to shape this study: Dr Peter Brennan, Professor Filippo Carla-Uhink, Dr Simon Corcoran, Dr Caillan Davenport, Dr Alan Dearn, Emeritus Professor John Drinkwater, Dr Michael Hanaghan, Dr Mark Hebblewhite, Professor Noel Lenski, Dr Carlos Machado, Dr Andy Merrills, Dr Oliver Nicholson, Dr Ted Nixon, Professor Roger Rees, Dr Umberto Roberto, Dr Paul Roche and Dr Christian Rollinger.