TRESS, GOTHIC ARCHITECTURE).
The principle of the arch has been known from very early times. When neolithic man discovered that a wide opening could be spanned by leaning two stones together at its apex, the first arch was made, and such triangular arches are widely found throughout the Mediterranean basin (for example, one at Alea in Arcadia; a similar triangular shape, though in corbelled construc tion is seen in the Gate of the Lions at Mycenae). The earliest known developed arches with curved sides that occur in the Tigro-Euphrates valley, at least as early as 400o B.C. In Egypt, also, the arch was known, although it was used only for utili tarian purposes. Almost all of these early examples are over drains, where the abutment question was simple, but in Asia, the Assyrians, at least, used the arch monumentally in gate ways. It was, however, in Italy, at the hands of the Etruscans, that the arch received its most important early architectural treatment, as in the famous gate of Perugia. Following the Etruscans the Romans (see ROMAN ARCHITECTURE) adopted the arch as perhaps the chief structural feature in the de sign of their monumental buildings and by them its use was spread all over the civilized world to become an integral feature of all the architecture succeeding them until the middle of the i 9th century. Since that tirne the discovery of the fact that iron, and later steel, could be formed into beams of great strength over long spans has reduced the use of the arch to a subsidiary and often merely decorative position.
For the different types of arch see the illustration and for its history the general articles under the headings of the various styles of architecture. See also ARCADE. (T. F. H.)