The Great Wall has three major components: passes, signal towers (beacons), and walls. The design of each of these features has been determined by strategic importance.

The body of the wall usually stood 21.3 feet (6.5 metres) wide at the base and 19 feet (5.8 metres) at the top, with an average height of 23 to 26 feet (7 to 8 metres), or a bit lower on steep hills.

Those responsible for the construction of the wall made maximum use of natural features and it is this that accounts for the dragon like appearance as the structure wends its way across the terrain. Mountains, rivers and sheer cliff faces were natural defences and these were enhanced by the wall rendering the boundary virtually impenetrable. The average height of the wall from the base upon which it was built was some 8 meters (26 feet) while it would be some 6.5 meters (21.3 feet) wide at the base tapering to 5.8 meters ( 19 feet) at the top. The materials used in the construction varied according to what was available on site. While some sections were composed of local stone or bricks with an infill of crushed rocks or earth, others would be of adobe or tamped earth between timbers. The contrasting styles of construction can be seen by comparing the stone faced walls near Badaling with the much less sophisticated rammed earth and adobe walls in the western desert region. The stone and brick construction permitted the builders to add a variety of refinements that gave the defending army cover and other advantages over their enemies. These included steps leading to the top of the ramparts where the outer side of the wall was crenelated to provide cover for archers. Openings enabled the guards to keep a look out for any threat of invasion. At regular intervals of approximately 200 to 300 meters (217 - 860 yards) platforms were set up. There were three different types designed to give the defenders a better viewpoint as well as being a vantage point from which to fire upon the enemy, especially if they were attempting to use scaling ladders.

Platforms

The first type was fairly simple with four walls topped with battlements for use by archers.

The second was normally brick built and of two storeys. The upper floor would be supported on a number of arches, while the outer facing walls had embrasures for archers. The rooms thus created were used by the soldiers as living quarters and store rooms. Depending upon the size of the platform access to the upper level could be by stairs or merely a rope ladder. The upper storey would provide for further archers to be posted and could also be used as a lookout or in view of its elevation could facilitate signaling to other guard positions along the wall. Signaling devices could vary from torches, to bells, clappers or gongs. The platforms had gates in them so that soldiers could move along the wall.

The third type was a substantial block house that was either square, oblong or even rounded. These were normally built where there was a steep cliff or precipice. It would be kept stocked with arms and ammunition.

There were some 1,200 blockhouses and watchtowers along the stretch of wall between Beijing and the Shanhai pass. The normal complement of men would be 60 including the officers. Their duties would be organised to include the guarding of the platform and the length of wall under their control. Large jars of gunpowder would be on hand, as well as a stock of arrows and other armaments and missiles that could be hurled down upon any attackers.

The chain of command along the wall varied somewhat during various stages of its history. Emperor Qin Shi Huang (Shi Huangdi of the Qin) had twelve prefectures along the Great wall and by contrast, during the Ming Dynasty it was organised as the Nine Border Garrisons. These nine sectors each had a commanding officer who would have been selected for both his administrative ability as well as his military skills.

When you visit the Great Wall of China, you can impress your fellow travelers with your expertise if you know a few words of Chinese that describe certain of the features:

Duo kou: ( ) This is the name for the crenelated battlements on the outer side of the wall. It provided cover for archers who were able to fire onto the enemy through specially constructed slits. These were narrow on the inside but wide on the outside so that the archers had the advantage of a wide angle of vision while enjoying maximum protection. These openings were set at a lower level for use by archers and higher up for lookouts.

Nu chiang: ( or ) This is the low parapet on inner side of the wall, usually one meter high. It is built for the safety of both men and horses.

The Single Parapet Wall: ( )These sections ran along steep ridges which formed a natural defence. Quite narrow compared with the more substantial stretches, this part of the structure varied between two to four meters in height. As the terrain formed a barrier the wall facilitated defence of the border by giving the Chinese soldiery the advantage of height and also cover should enemy forces try to make a crossing. The so-called 'Heavenly Ladder' that can be seen in Simatai (120 miles northeast of Beijing in the north of Miyun County) is a fine example. In mountainous country where there are rocky outcrops, natural undressed stone was used in the construction.

Barrier wall: ( )This is a row of embrasured walls built vertically to the main body of the Wall (Great Wall).

Ma dao: ( ) Ramps and ladders within the pass provided access for both horses and men to the top of the wall. The ramp is five to six meters wide with one-meter-high Nu chiang running on the inner side of it. The incline was approximately 30 degrees and to give the horses a foothold raised courses of bricks were set across the ramp. This was usually achieved by laying these rows of bricks side-on whereas the bricks were laid flat to form the main carriageway.

Drainage system: ( )Drainage channels and waterspouts were built at intervals through which the rain drained away. The waterspout usually extended for one meter beyond the wall and a stone receptacle below it ensured the water was directed away from the foundations.

Wen cheng: ( )This is the parapet shielding the top of a gate. It is usually built in a shape of " " on the main direction of approach of the marauders who could be a threat.

Luo cheng: ( ) This is the extended protection outside the gates of Wen cheng, often topped with a watch tower. So it is the first defensive wall against invaders.

Pu fang: ( ) This is a shelter, often made of wood, that protected the guards on a platform.

Chuen: ( ) This is a door leading to a flight of steps built into the body of the wall and giving access to the top and other structures such as the towers.