Having thus cleared the way, M. Fustel began to put together his materials for the great work of his life, the _Histoire des Institutions Politiques_, in its new form. He had issued one volume and prepared for publication a second when he was prematurely lost to the world. His pupils have, indeed, been able to put together a third volume from his manuscript and from earlier articles; and a fourth and fifth are promised us. But these fragmentary sketches, written many of them under the shadow of approaching death, are only slight indications of what M. Fustel might have done for mediæval history. Nevertheless, his work, incomplete as it is, is of the utmost weight and significance; in my opinion, it has done more than that of any other scholar to bring back the study of mediæval society, after long aberrations, to the right lines. We have to continue the work of inquiry along those lines, and in his spirit. “It is now,” said he, in the Preface to the _Recherches_, “twenty-five years since I began to teach; and each year I have had the happiness to have four or five pupils. What I have taught them above everything else has been to _inquire_. What I have impressed upon them is not to believe everything easy, and never to pass by problems without seeing them. The one truth of which I have persistently endeavoured to convince them is that history is the most difficult of sciences.” And again, in the Introduction to _L’Alleu_, “Of late years people have invented the word _sociology_. The word _history_ had the same sense and meant the same thing, at least for those who understood it. History is the science of social facts; that is to say, it is sociology itself.” “The motto he had chosen, a motto,” says one of his pupils, “which sums up his whole scientific life, was _Quaero_.”