"If you haven't climbed the Great Wall, you haven't seen China." Many of your friends who visited China before might have told you this. It is, indeed an experience of life. Who would leave the country without seeing the only construction that the American astronauts could recognise with their naked eyes, on their first flight to the Moon!

The Great Wall of China starts from Shanhaiguan Pass, a seaport along the coast of Bohai Bay in the east, to Jiayuguan Pass in Gansu Province in the west, covering 16 provinces, cities and autonomous regions in China. It is more than 6,000 Km long (one li=500 metres), hence the name "Ten Thousand-li-long Wall".

The Great Wall traverses many mountains and gullies, a countless number of inner walls, outer walls, fortified towers, signal beacon towers,fortifications and garrisons complete this complex, and make up the whole system of the Great Wall.

Those who succeeded in climbing the wall today are often regarded as "real heroes", from this we should realize the difficulty in climbing the wall, but can you imagine how even more difficult it is to build the Great Wall without modern machinery?

The bricks, rocks and lime used to build the Wall had to be carried up the mountains at the cost of back-breaking labor, morever, goats and donkeys carried the earth and bricks in baskets, some of the rocks were moved up slopes by means of rolling rods and hoisting bars. It is hard to calculate the amount of manpower used in the construction of the Great Wall.

In Beijing, the Great Wall is 629 Km long, five sections of the Great Wall have been opened to visitors. There are Badaling Section, Simatai Section, Mutianyu Section, Jinshanling Section and Gubeikou Section. Of all these five sections, the Great Wall at Badaling Section is the most famous and best preserved.

In ancient China, military information is usually conveyed through horsesiders and beacon-towers. In pain area, emergent military information is conveyed from one station to another by riding horses-at each station the horses should be changed and supplies refilled. Hopwever, in the Tang Dynasty, when the whole country is not at war, horses were used to carry fresh Lichii to Chang'an, the capital at that time for the emperor's most favorite concubine-Lady Yang Yuhuan. Du Fu, a famous poet in the Tang Dynasty wrote certain poems to criticise the corruption of the emperor.

In the mountainous area, on the other hand, it could ne extremely difficult for the horses to send messages, therefore, beacon towers were built along the wall to relay information from place to place. When the enemy invaded in the daytime, wolve's dung was used to burn for a strong smoke, while at night, beacon fires were lit on the towers to give a warning message. But you may ask why wolve's dung were used?

One reason is that there were many wolves in the region and wolve's dung could easily be found, another reason is that the wolve's dung gathered closely and went straight upward so it can easily be seen from afar. Moreover, the number of the smoke signals could reveal the numner of invading enemies. One smoke used to represent 100 enemies, two smokes, 500, and 3 smokes,1,000 etc, and the amount of smokes also expressed the degree of emergency.

It is evident that the purpose of building the wall was to prevent the frontier from the invasion of the norhtern nomadic tribes.