=Arbalestina.= In the military system of the Middle Ages, was a small window or wicket through which the cross-bow men shot their quarrels or arrows at an enemy besieging a fortified place. =Arbaletrier d’une Galere= (_Fr._). That part of a galley where the cross-bow men were placed during an engagement. =Arbalist=, or =Arblast=. A cross-bow man. =Arbela= (now _Erbil_). A city in Asiatic Turkey; near here was fought the third and decisive battle between Alexander the Great and Darius Codomanus which decided the fate of Persia, October 1, 331 B.C., on a plain in Assyria, between Arbela and Gaugamela. The army of Darius consisted of 1,000,000 foot and 40,000 horse; the Macedonian army amounted to only 40,000 foot and 7000 horse. The gold and silver found in the cities of Susa, Persepolis, and Babylon, which fell to Alexander from this victory, amounted to £30,000,000 sterling; and the jewels and other precious spoil belonging to Darius sufficed to load 20,000 mules and 5000 camels. =Arbourg.= A city in Switzerland, whose citadel, which was constructed in 1600, is an important depot for military stores. =Arbrier= (_Fr._). Stock of a cross-bow. =Arc= (_Fr._). A bow; an arch in building. =Arc à Jalet= (_Fr._). A small cross-bow, used to throw bullets, etc. =Arc, Elevating.= In gunnery, is an arc attached to the base of the breech parallel to the ratchets and graduated into degrees and parts of a degree. A pointer attached to the fulcrum points to the zero of the scale when the axis of the piece is horizontal. Elevations and depressions are indicated by the scale. Besides the graduations on the arc, the ranges (in yards) and the charges for shot and shells are given. =Arch.= In military architecture, is a vault or concave building, in form of a curve, erected to support some heavy structure, or passage. =Archers.= In military history, a kind of militia or soldiery, armed with bows and arrows. They were much used in former times. =Archery.= The use of the bow and arrow; the practice, art, or skill of archers; the art of shooting with a bow and arrow. =Arch-gaye=, or =Lance-gaye= (_Fr._). A lance used by the Gauls and Franks, which consisted of a sharp-pointed piece of iron attached to a light wooden handle. =Architonnerre= (_Fr._). A machine made of copper, which threw iron bullets with great force and noise; it was used in ancient times, being an invention of Archimedes. =Architrave.= The master-beam, or chief supporter, in any part of subterraneous fortification. =Arch, Triumphal.= In military history, is a stately monument or erection, generally of a semicircular form, adorned with sculpture, inscriptions, etc., in honor of those heroes who have deserved a triumph.