论北魏长城-军镇防御体系的建立

公元5世纪初，柔然崛起于大漠。在难以从根本上消除其威胁的情况下，为了防御柔然的侵扰，北魏先后3次大规模修筑长城。但是，长城作为单一的防线无法长久地阻挡柔然的骚扰和南侵，因此，北魏设置了众多军镇，构成统一有效的长城——军镇防御体系。

On the Defensive System of Great Wall--Military Town of Northern Wei Dynasty

At the beginning of 5 A.D., Rouran people grew up in the Mongolian Desert. Because it was difficulty to eradicate its threat, Northern Wei Dynasty thrice built Great Wall in large scale in order to defend Rouran's aggression and annoyance. But the Great Wall, as a unitary defensive line, could not blocked off Rouran's invasion for long. Therefore Northern Wei Dynasty built many military towns and formed a unitive Great Wall-Town defensive system.