求翻译：其三是，老北京的城墙，无论是外城、内城还是紫禁城，尽管其地基起伏不定，内外城墙高低有别，但各自的城脊却奇迹般地座落在同一水平线上，无一例外。这在世界测量史和建筑史上都是一个奇迹。是什么意思？

Third, the old Beijing city wall, whether it is outside the city, inner city or the Forbidden City, despite the ups and downs of its foundation, the level of internal and external walls are different, but each city is located in the spine, but miraculously the same level, without exception . Measure

It is 3, the old Beijing city wall, and whether it is outside the city or Forbidden City, despite its foundations, ups and downs, high or low walls inside and outside the country, but their respective city chiropractic miraculously located in the same horizontal line, there is no exception. This mea

Third is, old Beijing's city wall, regardless of is the outer city, the inner city or Forbidden City, although its ground fluctuation does not decide, the inside and outside city wall height has leaves, but respective city keel miracle is located actually in the identical level line, exists not one

Third, the old city walls of Beijing, both outer city and the inner city and in the forbidden city, despite fluctuating on its Foundation, inside and outside the city walls high and low is different from, but the respective city Ridge are miraculously is located on the same level, without exception.

Third, the old city walls of Beijing, both outer city and the inner city and in the forbidden city, despite fluctuating on its Foundation, inside and outside the city walls high and low is different from, but the respective city Ridge are miraculously is located on the same level, without exception.