Passes were defence fortifications in ancient China. Born of war, they were built at points of strategic importance.
In the early days passes were built of rammed earth and masonry at places easily defended and hard to be conquered. Later, cities were developed around the passes. Countless passes were built in ancient China. The nine best known ones are Shanhai Pass, Juyong Pass, Zijing Pass, Niangzi Pass, Pingxing Pass, Yanmen Pass, Jiayu Pass, Wusheng Pass and Youyi Pass.
The passes fall roughly in two types: those on the Great Wall and those on postal routes.
The passes built on the Great Wall were regarded as national defence facilities. At the eastern terminus of the Great Wall to the northeast of Qinhuangdao stands Sanhai Pass, which holds vital access between northeast and central China. It is billed as "No. 1 Pass on the Great Wall".
The passes on postal roads may be regarded as regional fortresses. A common feature about these passes is that virtually all of them were on provincial or county boundaries. Though not as large as those on the Great Wall, they were also strategically located for defence purposes. Major postal road passes in existence today are Loushan Pass of Guizhou, Jianmen Pass of Sichuan, Yanmin Pass of Shanxi, Tiemen Pass of Xinjiang, and Guimen Pass of Guangxi, which have all become popular scenic spots today.