WHEN my father was taken ill, on May 28th, 1935 -- it was the day on which his eldest son, Henri-Edouard, died -- he left on his table the three hundred pages of the manuscript of Mohammed and Charlemagne, which he had completed on May 4th.
This was the crowning achievement of his last years of work. The problem of the end of Antiquity and the beginning of the Middle Ages had always preoccupied him. Before the War, in his lectures on the History of the Middle Ages, he drew attention to the profound traces which the institutions of the late Roman Empire had left upon those of the Frankish epoch. But it was during his captivity in Germany, when, as a prisoner in the camp of Holzminden, he organized, for the many Russian students who shared his fate, a course of lectures on the economic history of Europe, that the solution of this capital problem seems to have dawned upon him. And during his exile in the village of Kreuzburg, in Thuringia, while he was writing his History of Europe, he emphasized, for the first time, the close relation that existed between the conquests of Islam and the formation of the mediaeval Occident.
The History of Europe, which he did not live to complete, was published only after his death. At that time no one was aware of the subject of the present volume.
My father, however, returning again and again to his study of the available sources, had never ceased to examine this problem, which was the great scientific interest of the last twenty years of his life.
In 1922 he published in the Revue belge de Philologie et d'Histoire a short article entitled "Mahomet et Charlemagne", which contained a statement of his thesis. He then expounded it before the International Historical Congress -- which met in Brussels in 1923 and in Oslo in 1928; it was also the subject of a course of public lectures delivered in the University of Brussels in 1931-1932, and of other lectures given in the following Universities: Lille ( 1921),