Paris is also known as the "city under the city" by the Paris catacombs and sewers cross-cutting component.

又被称为巴黎的“城下之城”，由巴黎地下墓穴和下水道交叉组成。

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At the most remote end of the crypt there appeared another less spacious. Its walls had been lined with human remains piled to the vault overhead , in the fashion of the great catacombs of Paris.

这个墓穴的远端连着另一个更小的墓穴，里面曾一直顺墙排满尸骨，照巴黎那些大墓窟的样子一直推到拱顶。

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Centuries later in Paris, catacombs emerged as a creative and discreet solution to a dire public health problem.

BBC: Exploring the history of catacombs

Of the sites below, only the Paris and Odessa Catacombs have small stretches that are legal to visit.

BBC: Discovering an unseen urban underworld

The catacombs are a by-product of Paris' early development.

CNN: Loving life in Paris' Empire of the Dead