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by CareyBot

If you've ever seen a picture of Stonehenge, the prehistoric monument near Salisbury, England, you'll recognize the structural system known as post and lintel. It consists of two upright blocks -- the posts -- with another block -- the lintel -- spanning the gap between them. This was the earliest type of structure used to span open space. The trouble was, the widest distance you could span with a post and lintel was limited to the size of the biggest stone lintel you could get your hands on -- not to mention lift into place. Hence, even the grandest ancient buildings under roof -- Egypt's vast temple at Karnak, for instance -- were little more than forests of stone columns with narrow passages left over in between. The invention that finally overcame this problem was the arch. ...