The ji (pronunciation: [tɕì], English approximation: // jee, Chinese: 戟; pinyin: jǐ) was a Chinese polearm, often translated into English as spear or halberd, though they are fundamentally different weapons. They were used in one form or another for over 3000 years, from at least as early as the Zhou dynasty, until the end of the Qing dynasty. They are still used for training purposes in many Chinese martial arts.
In the Song dynasty, several weapons were referred to as ji, but they were developed from spears, not from ancient ji. One variety was called the qinglong ji (Chinese: 青龍戟; lit. 'cerulean dragon ji'), and had a spear tip with a crescent blade on one side. Another type was the fangtian ji (Chinese: 方天戟; lit. 'square sky ji'), which had a spear tip with crescent blades on both sides. They had multiple means of attack: the side blade or blades, the spear tip, plus often a rear counterweight that could be used to strike the opponent. The way the side blades were fixed to the shaft differs, but usually there were empty spaces between the pole and the side blade. The wielder could strike with the shaft, with the option of then pulling the weapon back to hook with a side blade; or, he could slap his opponent with the flat side of the blade to knock him off his horse.
The Ji is popularized through a historical character known as Lü Bu. In the Romance of the Three Kingdoms, his weapon of choice was the fangtian huaji (方天画戟). The historical Lü Bu existed long before any known examples of the fangtian huaji, so he could not have used the actual weapon. It's possible he used some other weapon of unknown but similar construction, such as a more contemporary model of ji or ge. It's unknown whether the peculiarity of his weapon was a literary device used by Luo Guanzhong, the author. Since this novel was extremely influential during the Song dynasty, comparable to the influence of Homer throughout Europe, the Song-era polearm may have been named based on its similarity to, or in honor of, the weapon that was attributed to Lü Bu in this famous novel. This would be comparable to the famous semi-mythological origin story of the yanyuedao (偃月刀; lit. "reclining moon blade"), the weapon wielded by Guan Yu (關羽), another character from the novel and a real historical person. The first historical or archaeological evidence of this polearm comes from an 11th century illustration in the military manual Wujing Zongyao (武經總要). The yanyuedao came to be known as the guandao after its invention was anachronistically attributed to Guan Yu himself, due to his wielding the weapon throughout the Romance.
Scythed dagger-axe combined with a spear, forming a ji, Warring States period
Ji with back hook, Eastern Zhou
Ceremonial jis, Tang dynasty
A ji dao on the left from the Wujing Zongyao
Tomb figurines of a soldier and two men holding an axe and qinglong ji, Ming dynasty