急求一份介绍北京特色的英文文章

One of the largest building-construction projects ever carried out, it runs (with all its branches) about 4,000 mi (6,400 km) east to west from the Bo Hai (Gulf of Chihli) to a point deep in Central Asia. Parts of the fortification date from the 4th century BC. In 214 BC Shihuangdi connected existing defensive walls into a single system fortified by watchtowers
译：中国北方防御性的屏障，是人类建造的大规模建筑工程之一。东起渤海，向西延伸到中亚深处，若将其支段计算在内，总长约6,400公里(4,000哩)。其中部分堡垒的历史可追溯至公元前4世纪。公元前214年秦始皇将当时存在的城墙，连结成一整套防御体系，并设置了望台增强其功能。