每隔一定距离就建造一座烽火台，用来传递军情在长城的整个军事防御体系中，这一切都起着非常重要的作用。

Beacon towers were also built at fixed intervals for passing on military information. All these indicate the important role of the Great Wall in military defense.

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四十年来，北约的存在一直是以前苏联的军事威胁和西欧对更加坚实的防御体系的需要为理由。

For 40 years, its whole reason for existing was the military threat posed by the Soviet Union and Western Europe's need for stouter defences than it could provide alone.

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