This book is the result of a project that stretches back in time. Shortly after publishing my research paper “El servicio militar de los judíos en el ejército romano” [Jewish Military Service in the Roman Army] in 2003, I realized that many of the subjects I covered in it would need some revision and that there was growing interest in the subject. That is why, in spite of having received several gracious and generous offers to have that paper published in English—first from Jonathan P. Roth and, more recently, from Christopher B. Zeichmann—, I decided to revise and expand it in depth and to publish the results as a monograph. The time, however, was not ripe …

Years later, I received a grant from the Spanish Ministry of Science, Innovation and Universities as part of its study stay programme for senior professors and researchers in foreign institutions of higher learning and research, which is included in the Salvador de Madariaga programme. As a result, I had a research stay at the Faculty of Divinity of the University of Cambridge as a visiting fellow in Wolfson College, and I am grateful to its President, Professor Jane Clarke, for her warm welcome and for having put the resources of the College, whose staff was ever pleasant and efficient, at my disposal. The time had finally come for me to make inroads into my long-awaited project on the presence of Jewish soldiers in the Roman army, and I had the chance to present part of its results to the Hebrew, Jewish and Early Christian Studies Senior Seminar, directed by Professors William Horbury, Nicholas de Lange and James Carleton Paget. The exchange of ideas and suggestions during this Seminar allowed me to make significant improvements to my research. In addition to its convenors, I thank Irina A. Levinskaya (Russian Academy of Sciences) and Geoffrey Greatrex (University of Ottawa) for their thoughtful comments.

I never would have imagined that, for a number of reasons, this would be one of the hardest assignments in my academic career. My elder brother passed away during the first days of that stay, in the Michaelmas Term 2018, his will to live and the encouragements of his loved ones having been powerless in the face of death. For this reason, this book is dedicated to his memory, as my recollection of him, which was on my mind through every passing hour in the beautiful city of Cambridge, is indissolubly linked to it.

Among us the living, immersed in the daily struggle of our lives, ever full of problems and concerns, but also hope and joy, there are many people without whom this book would not have been possible. First of all, I would like to thank Professor Nicholas de Lange, my mentor and magister in Cambridge, from whom I have learnt so much, and whose humanity is without bounds. I still yearn for our endless conversations. Likewise, I cannot imagine a better host than Professor William Horbury, with whom I shared unforgettable moments at Corpus Christi College. His kindness and contagious joy are only matched by his awe-inspiring wisdom. Among the magnificent group from Cambridge, I must also mention Professors James Nicholas Carleton Paget, James K. Aitken, George van Kooten and Judith Lieu. It was an honour for me to have met them and for them to have shown an interest in my research. Until that moment, some of them had only been present in my academic dreams, but those dreams had finally come true.

I must also thank Professors Andrew Fear (University of Manchester), Christopher B. Zeichmann (University of Toronto), Javier Arce (Université Charles de Gaulle-Lille 3) and, again, Nicholas de Lange, for kindly accepting to read the first draft of this book. Their comments and timely corrections have been invaluable to me. Likewise, the thoughtful suggestions of Professor Domenico Vera (Università degli Studi di Parma) were of great value to me.

Moving on to Spain, I cannot forget the constant assistance I received from my colleague and friend, Sabino Perea Yébenes (UNED, Madrid). His critical spirit and his apt and timely suggestions are and have been a constant source of encouragement for me. Thank you, Sabino. The careful reading made by my other colleague-cum-friend, Fernando Bermejo Rubio (UNED, Madrid), has been no less invaluable. His astute and intelligent observations have “inevitably” enriched the end-result of this work. Thank you, Fernando.

I am also thankful to Mr. Michael Eric Moss for his excellent English translation and careful revision of the text of this book, as well as to Dr. David Soria Molina for his invaluable help with the prosopographic map.

Now that my work is finally over (or has it only begun?), I hope the results are worthy of the noble motives that gave rise to it and, especially, of the extraordinary people who inspired it …

… As always, my wife, Ana, has supported me and helped me—as no one else could—throughout this exciting adventure.