Qin Shihuang, a historical figure, was very serious about military-related facilities, although his historical evaluation was mixed. At that time, the highways running through the three provinces also had the nature of military facilities in a strict sense. Therefore, both construction materials and construction technology are extremely rigorous. It is understandable that there are still no weeds after more than 2000 years of wind, frost, rain and snow.

As we all know, soil is the basic premise of vegetation growth, and when this road was built, the soil used was only used in the project after being cooked by fire, and the soil cooked at high temperature lost the basic conditions for vegetation growth. After all, water and fertilizer are lost in the process of fire roasting, which can't meet the demand of vegetation for growing environment and conditions, so it is also this reason that the grass will never grow.

In addition to the reason why the soil is burnt by fire, white cement and lime are mixed together for construction, and are divided into different construction bases in the process of road construction. After professional construction and rolling, the whole pavement is extremely strong, and it is extremely difficult to grow grass, or artificially create harsh soil conditions to avoid this hard-won road being swallowed up by weeds. Even now, such a rigorous construction process and technology are difficult to achieve.

Of course, in the northwest where the whole highway is located, the geological conditions are not suitable for the growth of vegetation. Salinity and desertification seriously limit the growth of vegetation. In addition, the whole construction supervision is extremely strict, and there is no situation of cutting corners. Therefore, weeds still do not grow, which is an intuitive witness to the construction quality.