请将下面这段话翻译成英文：

　　建造长城是为了防御来自蒙古的北方人侵者。多年来，人们已经建造了一些较矮小的城墙，但是秦始皇决定建造一座巨大的城墙来保卫他北边的疆土。长城始建于秦朝，后续的朝代进行继续建 造。后来，明朝重建了长城。我们今天所说的长城绝大部分都是明朝建造的。长 城是由农民、奴隶、犯人以及皇帝决定惩罚的人建造的。

　　参考答案:

　　The Great Wall was built to defend against the northern invaders from Mongolia. Smaller and shorter walls had been built over the years, while Qin Shi Huang decided to build a single giant wall to protect his northern borders. The construction of the Great Wall started in the Qin Dynasty and the following dynasties continued to work on it Later, the Ming Dynasty rebuilt the wail Most parts of the so- called Great Wall today was built in the Ming Dynasty. The wall was built by peasants,slaves, criminals, and other people that the emperor decided to punish.