Millions of tons, one would imagine. http://www.archiplanet.org/wiki/Great_Wall_of_China

a LOT

between 700,000,000,000 kg/m³ and 70,000,000,000 kg/m³ (very low estimate): 1) "The Great Wall stretches over approximately 6,400 km (4,000 miles) from Shanhaiguan in the east to Lop Nur in the west, along an arc that roughly delineates the southern edge of Inner Mongolia, but stretches to over 6,700 km (4,160 miles) in total." "Before the use of bricks, the Great Wall was mainly built from Earth or Taipa, stones, and wood. During the Ming Dynasty, however, 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. Stone can hold under its own weight better than brick, but is more difficult to use. Consequently, stones cut in rectangular shapes were used for the foundation, inner and outer brims, and gateways of the wall." "More than 60 kilometres (37 mi) of the wall in Gansu province may disappear in the next 20 years, due to erosion from sandstorms. In places, the height of the wall has been reduced from more than five meters (16.4 ft) to less than two meters. The square lookout towers that characterize the most famous images of the wall have disappeared completely. Many western sections of the wall are constructed from mud, rather than brick and stone, and thus are more susceptible to erosion." "The Great Wall is a maximum 9.1m (30 ft) wide" Source and further information: http://en.wikipedia.org/wiki/Great_Wall_of_China 2) "If you took all the bricks from the Ming portion of the Wall alone, they could circle the Earth at the equator in a wall five feet high and three feet thick." "The Great Wall's height averages from 15 to 30 feet high it's width averages from 15 to 25 feet wide with about a 13-foot wide roadway on top." Source and further information: http://library.thinkquest.org/C004471/tep/en/cultures/chinese.html 3) "The exhibition brought together all sixteen "inscribed bricks" discovered to date at sections of the wall in Beijing and Hebei. The inscriptions on these bricks, which measure 40 cm x 20 cm x 10 cm, provide valuable information regarding the construction of the Ming section of the wall" Source and further information: http://www.chinaheritagenewsletter.org/features.php?searchterm=001_greatwall.inc&issue=001 Further information: - "Ancient Wonder, Modern Challenge" http://www.friendsofgreatwall.org/DisplayText_cn.asp?TextID=90&page=&Class=10 4) "At the western end of the Ming Great Wall, a most well-preserved pass, Jia Yu Guan, stands solemnly in the gobi desert. And if you ask the local guides, they will direct you to a special brick. It is said that the designer of the pass in the Ming Dynasty (1368-1644) was so precise as to be able to calculate how many bricks would be needed for the construction. Upon completion of the pass, the surplus was only by one brick." Source and further information: http://www.thegreatwall.com.cn/en/goc/goc-4.htm 5) "In November 1998, China's Xinhua news agency announced the discovery of a previously unknown segment of the Great Wall of China in the Ordos (Maowusu) Desert in the Hui Autonomous Region of Ningxia, about 700 km (435 miles) west of Beijing. The segment's length is 25 kilometers (15.5 miles). The current Wall is the amalgamation of fortifications built by various ruling dynasties, especially the Qin and the Ming. Including its branches and extensions, the Wall runs from east China to its west - from Shanhai Pass near the Bo Hai (Gulf of Chihli) to Jiayu Pass in Gansu province - a distance of 7,300 km (4,500 miles). Without its secondary sections, it stretches for 6,700 kilometers (4,163 miles). The Wall's average height is 10 meters and its average width is 5 meters. Only 30% of it is in good repair, according a study published in December 2002 by the China Great Wall Academy. The masonry of the Wall has been eroded by nature and recycled into newer construction by Man." Source and further information: http://samvak.tripod.com/factoidg.html 6) "The Great Wall is 7.8 meters high and 6.5 meters wide at its base, narrowing to 5.8 meters on the ramparts, wide enough for five horses to gallop abreast." "In the Ming Dynasty, bricks were produced in kilns set up along the wall, which 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 as well as bear more weight and endure better than rammed earth. Compared to other materials, the bricks possess own advantages. Take stone for example, it can hold under its own weight better than brick, but is more difficult to use. Thus, stones cut in rectangular shapes were used for the foundation, inner and outer brims, and gateways of the wall. Stone Battlements line the uppermost portion of the vast majority of the wall, with defensive gaps" 7) "Some statisticians calculated that the great wall of China is made out of 3,873,000,000 bricks." ---------------- EVALUATION ---------- 1. Let's use point 5 length (with branches and extensions: 7,300 km (alternatively, without secondary sections: 6,700 km) 2. Let's use point 6 average section: 7.8 *(6.5 + 5.8)/2 = 48 m² (Alternatively, one could use point 5: 10*5= 50m²) This yields a total volume of about: 365,000,000 m³ (alternatively, about 350,432,160 m³) On the other hand, an inscribed brick measures: 40 cm x 20 cm x 10 cm = .4 * .2 * .1 = 0.008 m³ It it were only made of bricks, the number of bricks would be: 365,000,000 m³ / 0.008 m³ = 45,625,000,000 bricks (alternatively, about 43,804,000,000 bricks) That is more than ten times the "statisticians" evaluation in point 7. But maybe they considered the fact that a big part of the structure was made of stone or mud. And took also the erosion into account!!! Moreover, there are also some lower places for the road in the middle of the wall. So the total volume would be somewhere between 350,000,000 m³ and 35,000,000 m³ (very low estimate). "The density of solid clay bricks is around 2000 kg/m³" http://en.wikipedia.org/wiki/Brick Further densities: "Stone (common, generic) 2515 " "Mud, packed 1906" http://www.simetric.co.uk/si_materials.htm For an average density of around 2000 kg/m³ , the total weight would be between 700,000,000,000 kg/m³ and 70,000,000,000 kg/m³ (very low estimate).