What is the earliest meaning of "don't cross the line"

"Lei Chi" first refers to a water area in Leichi Township, Wangjiang County, located on the north bank of the middle and lower reaches of the Yangtze River. Leishuiyuan comes from Huangmei County, Hubei Province, enters the lake via Susong, and flows 15 miles southeast of Wangjiang County, hence the name Lei Chi. Because the Yangtze River waterway from Jiujiang to Nanjing is also the throat of Huangmei, Susong and Taihu River inland shipping, the situation is dangerous, so it is a battleground for military strategists in past dynasties.

The original intention of "not crossing the line one step" is to ask Jiangzhou Cishiwenqiao to take the defensive and not cross the line to Kyoto. Now it means not to go beyond a certain limit and scope.

Source: Liang Liang, the Prime Minister of the Eastern Jin Dynasty, wrote a letter to Wen Qiao: In the second year of Jinxianhe, Liyang was the satrap of Soviet rebellion, and Jiankang (now Nanjing), the capital of the Eastern Jin Dynasty, was besieged. Wen Qiao, the general of Pingnan, prepared to lead an army to help him in search of Yang, and wrote back to dissuade him: "I am worried about the Western Heaven and tired of my grandson, and I have never crossed the line." (See Biography of the Book of Jin and Yu Liang).

In the second year of Xianhe (327), Liyang Town (now Hexian County) and Shouchun Town (now Shouxian County) jointly rebelled and captured Kyoto Jiankang (including Nanjing). Jiangzhou Cishiwenqiao, loyal to the imperial court, wanted to quickly organize troops to defend Jiankang. Geng Liang, who was in charge of the central government in Jiankang, was worried that Tao Kan, a well-armed Jingzhou secretariat, had an opportunity. So he said in Wen Qiao Ji: "I was worried about Xiqiao and never crossed the line." It means Wen is in the original defense, don't cross the line and go east. Later used to indicate an insurmountable range. This is the origin of the idiom "Don't dare to cross the line".