The large, metal, cubic-shaped jungle gym was once common on playgrounds, but it led to injuries when children hit their heads on the bars or swung on them improperly, causing bruises, sprains, and fractures. It is more common now to find rope constructions similar in function, or wooden platforms with ladders and railings around the outer edges.
The first jungle gym was invented in 1920 and patented by lawyer Sebastian Hinton in Chicago. It was sold under the trademarked name Junglegym. The term "monkey bars" was first documented in 1955, though Hinton's initial patent of 1920 appeals to the "monkey instinct" in claiming the benefits of climbing as exercise and play for children.Hinton's chief goal, however, was to enable children to achieve an intuitive understanding of 3-dimensional space through a game in which numbers for the x,y, and z axes were called out and each child tried to be the first to grasp the indicated junction. Thus the abstraction of Cartesian coordinates could be grasped as a name of a tangible point in space.
One common type of jungle gym, shown at right, is a row of overhead bars, high enough for a child to hang from them but not so high as to cause serious injury in a fall. A child can "walk" hand-over-hand from one end to the other.
To reduce the risk of injury from falls, jungle gym areas often have a thick layer of wood chips or other impact-absorbing material covering the ground; the National Safety Council recommends that playgrounds have at least 12 inches (30 cm) of such material.