I do not indeed wish to be understood as maintaining that the religion of the Roman was the most important element in his mental or civic development: far from it. I should be the first to concede that the religious element in the Roman mind was not that part of it which has left the deepest impress on history, or contributed much, except in externals, to our modern ideas of the Divine and of worship. It is not, as Roman law was, the one great contribution of the Roman genius to the evolution of humanity. But Roman law and Roman religion sprang from the same root; they were indeed in origin _one and the same thing_. Religious law was a part of the _ius civile_, and both were originally administered by the same authority, the Rex. Following the course of the two side by side for a few centuries, we come upon an astonishing phenomenon, which I will mention now (it will meet us again) as showing how far more interest can be aroused in our subject if we are fully equipped as Roman historians than if we were to study the religion alone, torn from the living body of the State, and placed on the dissecting-board by itself. As the State grew in population and importance, and came into contact, friendly or hostile, with other peoples, both the religion and the law of the State were called upon to expand, and they did so. But they did so in different ways; Roman law expanded _organically_ and intensively, absorbing into its own body the experience and practice of other peoples, while Roman religion expanded _mechanically_ and extensively, by taking on the deities and worship of others _without any organic change of its own being_. Just as the English language has been able to absorb words of Latin origin, through its early contact with French, into the very tissue and fibre of its being, while German has for certain reasons never been able to do this, but has adopted them as strangers only, without making them its very own: so Roman law contrived to take into its own being the rules and practices of strangers, while Roman religion, though it eventually admitted the ideas and cults of Greeks and others, did so without taking them by a digestive process into its own system. Had the law of Rome remained as inelastic as the religion, the Roman people would have advanced as little in civilisation as those races which embraced the faith of Islam, with its law and religion alike impermeable to any change.[3] Here is a phenomenon that at once attracts attention and suggests questions not easy to answer. Why is it that the Roman religion can never have the same interest and value for mankind as Roman law? I hope that we shall find an answer to this question in the course of our studies: at this moment I only propose it as an example of the advantage gained for the study of one department of Roman life and thought by a pretty complete equipment in the knowledge of others.