A close order formation is a military tactical formation wherein soldiers are close together and regularly arranged for the tactical concentration of force. At about the time of the American Civil War (1861–1865), such combat formations of soldiers became uncommon, when improved small arms and artillery made a death trap of open ground for any formation so exposed. Hence, the technological concentration of much firepower to fewer soldiers rendered the close order formation obsolete by the end of the 19th century. Images from the Sumerian kingdom from the third millennium BC clearly show men with spears in close order formation. The close order tradition continued in the ancient world with the phalanx formation of first the Greeks and later the Macedonians. The Greek phalanx fought with the aspis, a large round bronze faced shield and a large spear. Frontage per man was the width of the shield (about 3 ft.) and normal formation depth four to eight men. The later Macedonian phalanx used a smaller shield but replaced the spear with a sarissa, a long pike used in two hands. Normal frontage per man remained the same but normal depth grew to 16 ranks. An innovation was the introduction of a "locked shield order" (synaspismos) with a frontage of only about 18 inches. The Roman legions also fought in close order, using the pilum and gladius, on a similar frontage per man to the phalanx. In the early Middle Ages, infantry used the shieldwall, a formation where shields were held edge-to-edge or overlapped. Close order was routinely used by infantry in the later Middle Ages, the intention being to avoid the enemy penetrating and disrupting their formation. A common literary image was that an apple should not be able to pass between their lances. In the 15th. century, the Swiss developed pike tactics which used closely packed deep columns. A reconstruction of the deployment of Zürich forces in 1443 gives a formation 56 men wide by 20 deep, the formation having a width of 168 ft. and a depth of 140 ft. The Swiss main formation at the Battle of Morat consisted of 10,000 men and experiments have estimated its area of as little as 60m. X 60m. The knightly cavalry of the Middle Ages could also fight in close order, stirrup to stirrup.