半月形的軍陣。
古(gu)代陣(zhen)(zhen)法,全(quan)軍(jun)呈弧形(xing)(xing)配置(zhi),形(xing)(xing)如彎月,是一種(zhong)非對稱的(de)(de)陣(zhen)(zhen)形(xing)(xing),大(da)將本陣(zhen)(zhen)通常位于月牙內凹(ao)的(de)(de)底(di)部。作戰時注重攻擊側翼,以厚(hou)實的(de)(de)月輪(lun)抵擋敵(di)軍(jun),月牙內凹(ao)處看(kan)似薄弱(ruo),卻(que)包藏兇險,大(da)將本陣(zhen)(zhen)應(ying)有較強(qiang)的(de)(de)戰力,兵強(qiang)將勇者(zhe)適(shi)用,也(ye)適(shi)用某些不對稱的(de)(de)地(di)形(xing)(xing)。
《新五代史·雜傳·杜重(zhong)(zhong)(zhong)(zhong)威(wei)》:“安重(zhong)(zhong)(zhong)(zhong)榮反,重(zhong)(zhong)(zhong)(zhong)威(wei)逆戰(zhan)於(wu)宗城,重(zhong)(zhong)(zhong)(zhong)榮為偃月陣(zhen),重(zhong)(zhong)(zhong)(zhong)威(wei)擊之不動。”
《續(xu)資治通鑒·宋(song)高宗紹興三十二(er)年(nian)》:“右(you)翼軍繼步軍北引而(er)東,作偃(yan)月陣,步軍居中(zhong),騎軍據(ju)其兩(liang)端,使賊(zei)不見首尾(wei)。”