The 8,851 km-long-wall, an architectural marvel and engineering feat of epic proportions, has stood the test of times, over millennia. The Great Wall of China, the largest man-made structure in terms of mass and surface area, lies on an arc that separates China from Mongolia. One of the seven Modern Wonders of the World, it snakes its way through hills, plateaux, plains, swamps, rivers, gorges and every kind of imaginable terrain and topography. The massive wall, the construction of which began in the 5th century BC during the Qing Dynasty as a defence stronghold to protect the country from invaders, was built and rebuilt over several generations, using stone and earthen fortifications. However, much of what survives today was built during the Ming Dynasty and in subsequent decades of the 16th century.
Walls, passes and signal towers or beacon fire sites constitute the three components of the structure. The height and width of the wall itself, which took shape to meld with the differing terrain, vary from place to place. Whereas its height ranges from 20 to 30 feet, its 21 feet wide base tapers to 19 feet at the top.
Because of the gargantuan size of the wall, and the difficulty in transporting building materials, locally available raw materials were used to build various sections. Stones, easily available in mountainous regions, were used in such areas, while rammed earth was used in the plains. In certain segments, river dikes, cliffs and gorges serve as wall and continue alongside the man-made structure.
However, much of the wall as it exists in present times, has been the handiwork of the Ming Dynasty. The Ming rulers undertook its massive reconstruction and enhanced it with sophisticated designs using huge quantities of brick and granite.
Rammed earth as building material was kept to a minimum. The watch towers were redesigned and modern cannons were mounted in strategic areas. In Beijing, which was the capital of the Ming Dynasty, and its vicinity, the wall was especially reinforced with lime and tile plastering, to make it impenetrable. Foundation, gateways and brims were renovated with rectangular stone blocks.
Protective segments
Passes served as major protective segments along the wall, and came to be located at strategic junctions, connecting trade routes. They were secured with ladders and ramps for the movement of soldiers and horses, and were fortified with inner and outer parapets, the former to prevent them from toppling over. The ramparts of the passes were strengthened with bricks and stones.
Three types of towers
Three types of towers, each with a specific purpose, were built along the route. The first kind is as high as the wall, and is prominently projected outside the wall. Its outer edge is a battlement. A berth on the tower sheltered soldiers from wind and rain. A second type of tower is two-storeyed with brick barracks built in the lower floor to house soldiers. The upper floor, built of brick walls and wooden pillars, has rooms and battlements with facilities to light beacon fires. A third kind of tower was built in strategic locations and served as storehouses for arms and ammunitions.
The beacon fire sites or signal towers, formed an important defence installation of the wWall. They were high bastions, usually located on hilltops, and placed 18 km apart from each other. They were built of stones or rammed earth, or from a combination of bricks and stones. Smoke, during day time, and fire, or lanterns at night, were used as signals from these vantage points. The lower tier of these twin-storeyed towers served as restrooms for soldiers, stables for horses and as storeroom for ammunitions.