Close order formation
（重定向自Close order）
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.