The Great Wall is the world's longest human-made structure, stretching 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. It is also the largest human-made structure ever built in terms of surface area and mass. At its peak the Ming Wall was guarded by more than one million men. It has been estimated that somewhere in the range of 2 to 3 million Chinese died as part of the centuries-long project of building the wall. The following three sections are in Beijing municipality, which were renovated and which are regularly visited by modern tourists The "North Pass" of Juyongguan pass, known as the Badaling. When used by the Chinese to protect their land, this section of the wall has had many guards to defend China’s capital [Beijing]. Made of stone and bricks from the hills, this portion of the Great Wall is 7.8 meters (25.6 ft) high and 5 meters (16.4 ft) wide. One of the most striking sections of the Ming Great Wall is where it climbs extremely steep slopes. It runs 11 kilometers (7 mi) long, ranges from 5 to 8 meters (16–26 ft) in height, and 6 meters (19.7 ft) across the bottom, narrowing up to 5 meters (16.4 ft) across the top. Wangjinglou is one of Jinshanling's 67 watchtowers, 980 meters (3,215 ft)above sea level. South East of Jinshanling, is the Mutianyu Great Wall which winds along lofty, cragged mountains from the southeast to the northwest for approximately 2.25 kilometers (about 1.3 miles).It is connected with Juyongguan Pass to the west and Gubeikou to the east 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. Battlements line the uppermost portion of the vast majority of the wall, with defensive gaps a little over 30 cm (one foot) tall, and about 23 cm (9 inches) wide. The steps that form the Great Wall of China are very steep and tall in some areas. Tourists often become exhausted climbing the wall and walk no more than a kilometer or two (around a mile).