a case in point is that的意思是什么

造句：

1. The Great Wall is a good example. It was also an important military defense construction. It spanned 15 provinces and cities to protect the security of the Qin Dynasty.

   长城就是一个很好的例子。它也是一项重要的军事防御建设。它横跨十五个省市，保卫秦朝的安全。