請將下面這段話翻譯成英文：

　　建造長城是為了防御來自蒙古的北方人侵者。多年來，人們已經建造了一些較矮小的城墻，但是秦始皇決定建造一座巨大的城墻來保衛他北邊的疆土。長城始建于秦朝，后續的朝代進行繼續建 造。后來，明朝重建了長城。我們今天所說的長城絕大部分都是明朝建造的。長 城是由農民、奴隸、犯人以及皇帝決定懲罰的人建造的。

　　參考答案:

　　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.