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other signs, play only a strategic and military role from the stand- point of attack and defense. These are only a historical form, secondary and subordinate in the formation of frontiers. They intervene in the fixation of limits only in order to perturb, by artificial means and by force, the real natural boundaries of social groups boundaries which are above all social and positive. The military boundaries established in order to favor not only defense, but offense, are far from representing, as we shall see, the reciprocal limits of intersocial actions and reactions.
If neither rivers, seas, oceans, nor mountains, nor even, at certain times, deserts, can prevent continued variations of the intersocial equilibrium, we can then understand the meaning of the evolution of the sign-indicators of frontiers. This evolution is effected by transferring the most apparent physical forms into more and more ideal symbolical signs. This very evolution is favored by the fact that between a great many groups there do not exist any physical or geographical phenomena as considerable as those which have furnished the basis for the theory of the natural frontiers. To illustrate, there are six trees of colossal size still existing in Mexico, being a species of magnolia, at least six hundred years old, which formerly served as the frontier of the state of the ancient king of the Zapotecs. We can still admire them at Etla, Teozacualco, Zaniza, Santiaguito, and Totomo- chapa. These boundaries were fixed through traditions, that is, through custom and even through formal treaties. When it was a question of establishing limits of this kind, the witch-doctor was called in, who executed some magic ceremonies by beating a drum called maraca a drum peculiar to all the savage people of America and by smoking long cigars, doubtless in order to drive away, by the noise and smoke, the hostile and malignant spirits. Sometimes baskets, rags, and bits of bark were sus- pended from these trees in order to render the frontiers visible, violation of which was a frequent cause of war. This rag is the ancestor of the flag around which are still grouped our national forces whose colors are represented upon the boundary posts of modern nations. Among the Murras there appears also to have been a certain understanding in reference to the possession of
