4H THE AMERICAN JOURNAL OF SOCIOLOGY
of the military marches, it is here that are formed the military centers of new states which at certain times become the centers for the formation of new military states.
Since at the frontiers the civil authority was confused with the military power, the boundary line was fortified. Garrisons and fortresses were increased upon the Danube as far as the sea, and behind this first defensive line six hundred strong places were put in a state of defense in Dardania, in Thrace, in Macedonia, in Epirus, and in Thessaly. The mountains and rivers were not, as a matter of fact, even military frontiers, except as they were defended, just as the sword does not become a weapon until it is taken in hand. Still farther toward the interior, the defiles, of Thermopylae, the isthmus of Corinth, the Chersonesus of Thrace, and the Crimea were barred by long walls. Already the emperor Anastasius had erected them from the Black Sea to the Sea of Marmora in order to defend Constantinople; and in Asia the same thing was done between Trebizond and the Euphrates; a long line of fortresses extended along the Persian frontier. Africa itself was covered with strongholds. It was not that rivers and mountains were lacking, but that they were ineffective as social frontiers, because they are not social nor even military frontiers. They are rendered secure only upon condition of being fortified ; that is to say, by social, even merely military, frontiers. They are secured only by being fortified or crossed; and even then this is only from the military point of view, which itself is subject to all the fluctuations of other social forces from without and from within.
Thus true military marches were established; the com- manders of these marches lacked only sovereignty, and even this was delegated to them. In the echelonned places of the limes bands of stationary limitanei held garrison; dues were placed in authority over the guards of the marches, with com- manders of militia at their head. Only with this difference from the period of the Roman Empire that the fortifications and garri- sons were no longer solely at the extreme frontiers; the whole Byzantine Empire was covered with them. It was a sign of evi- dent weakness; but it prevented neither the Slavs, nor the
