Great+Wall+of+China

[|Great Wall of China] - a series of fortifications made of stone, brick, tamped earth, wood, and other materials, generally built along an east-to-west line across the historical northern borders of China in part to protect the Chinese Empire against intrusions or military incursions. Several walls were being built as early as the 7th century BC. Later they were joined together and made bigger, stronger, and are referred to as the Great Wall.

The Great Wall has been rebuilt, maintained, and enhanced. The majority of the existing wall was reconstructed during the Ming Dynasty. The Ming walls measure 8,850 km (5,500 mi). This is made up of 6,259 km (3,889 mi) sections of actual wall, 359 km (223 mi) of trenches and 2,232 km (1,387 mi) of natural defensive barriers such as hills and rivers.


 * The only work built by human hands on this planet that can be seen from the moon, the Wall constitutes, on the vast scale of a continent, a perfect example of architecture integrated into the landscape.

Before the use of bricks, the Great Wall was mainly built from rammed earth, stones, and wood.
 * What's the problem?**
 * **Ask** - Why was rammed-earth used originally? What were some of the problems with using rammed earth?
 * **Imagine** - What alternative building materials were available during the time when the Great Wall was being constructed? How would these improve the wall construction?
 * **Design, Build** - During the Ming Dynasty, bricks were heavily used in many areas of the wall, as were materials such as tiles, lime, and stone. The size and weight of the bricks made them easier to work with than earth and stone, so construction quickened. Additionally, bricks could bear more weight and endure better than rammed earth.
 * **Improve** - Stone can hold under its own weight better than brick, but is more difficult to use. Stones cut in rectangular shapes were used for the foundation, inner and outer brims, and gateways of the wall.


 * That's engineering**
 * [|brick] - a man-made building material used to make walls and make places to walk. Bricks are made of clay. Bricks are either formed into molds and then baked in an oven. The color of a brick depends on the color of the clay from which it was made. The bricks are joined together using mortar.


 * [|defensive wall] - a fortification used to defend a city or region from potential aggressors. Walls, such as the Great Wall of China, Hadrian's Wall,  extended far beyond the borders of a city and were used to enclose regions or mark territorial boundaries. Beyond their defensive utility value many walls also had important symbolic functions — representing the status and independence of the communities they embraced.

> wall-building, rammed earth, gravel, board frames, earthen work, stone, bricks, tile, dike, moat,
 * Engineering ideas**

Challenges for you to work on...
 * Do It**
 * [|Great Wall of China - virtual tour] - the large picture can be rotated, panned ans zoomed.


 * News, updates**


 * Learn more...**
 * [|UNESCO World Heritage Listing] - example of a military architectural ensemble which served a single strategic purpose for 2000 years, but whose construction history illustrates successive advances in defence techniques and adaptation to changing political contexts.

..r0