关于长城的英语句子可归纳为以下五类，涵盖其历史、长度、特征及保护等核心内容：

一、历史起源

The Great Wall was built during the Qin Dynasty to protect China's northern border.

（长城始建于秦朝，用于守护中国北部边疆。）

二、长度与规模

The Great Wall stretches over 5,000-6,000 kilometers, with the most famous sections （e.g., Badaling, Mutianyu） totaling over 13,000 kilometers.

（长城总长约5,000-6,000公里，其中八达岭、慕田峪等段合计超13,000公里。）

三、建筑特征

The walls are made of stone and brick, with a height of 2-3 meters, allowing horses to walk shoulder to shoulder.

（城墙由石砖建成，高度2-3米，可并行骑马。）

四、文化象征

The Great Wall is a symbol of China's historical strength and architectural ingenuity, often described as a "gigantic dragon winding through mountains."

（长城是中国历史与建筑智慧的象征，常被比作“盘踞山间的巨龙”。）

五、保护与现状

It remains a UNESCO World Heritage site and a popular tourist attraction, with ongoing efforts to preserve its structural integrity.

（作为联合国教科文组织世界遗产，长城是热门旅游地，正通过保护工程维护其原貌。）

说明：以上信息综合自权威来源，涵盖历史背景、数据统计、建筑细节及文化意义，可满足不同场景的英语表达需求。