PERHAPS the scope of this book will be best understood if I explain that the subject attracted my attention, not as an important crisis in the history of Ireland, but, in the first place, as an appendix to the history of the Roman Empire, illustrating the emanations of its influence beyond its own frontiers; and, in the second place, as a notable episode in the series of conversions which spread over northern Europe the religion which prevails to-day. Studying the work of the Slavonic apostles, Cyril and Methodius, I was led to compare them with other European missionaries, Wulfilas, for instance, and Augustine, Boniface, and Otto of Bamberg. When I came to Patrick, I found it impossible to gain any clear conception of the man and his work. The subject was wrapt in obscurity, and this obscurity was encircled by an atmosphere of controversy and conjecture. Doubts of the very existence of St. Patrick had been entertained, and other views almost amounted to the thesis that if he did exist, he was not himself, but a namesake. It was at once evident that the material had never been critically sifted, and that it would be necessary to begin at the beginning, almost as if nothing had been done, in a field where much had been written.