Trench bridgeThe trench bridge was used to pass through obstacles such as moats or moats outside the city, and served as a temporary bridge for the mobility of the besieging army.

Since the Warring States Period, there has been a record of the use of moat bridges in China, which is called "Flying River" or "Flying Bridge". According to the book "Liutao? Tiger Tao? The record of "Military" has: "Crossing the ditch and flying bridge, one is one zhang five feet (4.7 meters) wide, two zhang (6.26 meters) long and above, with turns, rollers, and eight bodies, and is opened by Huanlitong. It can be seen that before the Song Dynasty, China was extremely mature in the development of moats, not only the use of pins, rollers and other mechanical devices, the width of the bridge is up to one zhang and five feet, if eight are used at a time, it can provide a front of up to 12 zhang (37.56 meters) wide for the troops to pass through.

In the Song Dynasty, the moat bridge was generally equipped with wheels and made into a car model for easy migration. There are a total of five kinds of moat bridges in the Song Dynasty, and the width of the moat is determined by the width of the moat or moat, and most of these moats and bridges were made from local materials after the attackers observed during the siege. For the convenience of transportation, there are two large wheels under the abutment of the moat bridge, so that the besieging army can deploy the moat bridge by surprise, so that the troops can quickly pass through the bridge deck and carry out storming operations. In order to ensure the stability of the bridge deck, there are two small wheels at the front end of the moat bridge to make the bridge more stable when the small wheels sink into the soil on the opposite bank, which is obviously more advanced than the previous method of fixing with many ropes.

It is recorded in the Tang soldier's book "Taibai Yang Jing" that the moat is as wide as two zhang. It is not easy to find huge timber in the manufacture of moats; When the bridge is too long, it is also inconvenient to use. Therefore, when the ditch or moat is too wide, a folding bridge with a more complex mechanism is used.

A folding bridge is a method of connecting two moat bridges to make up for the lack of length. The structure of the folding bridge has a turnaround (pin) and a roller (winch), the turnkey is used to connect the two bridge decks, and the roller is used to control the pitch of the extension bridge deck. It must be noted here that there are some differences between the plates of the folding bridge on the Hongzhiben and the Sikuben of the "General Essentials of the Wujing", and because the plate of the Hongjiben is not very reasonable, the plate description of the Sikuben is used here.

When moving, fold the two sections; When in use, the trench bridge is pushed into the trench and the two sections are opened to form a long bridge. The wheels under the trench bridge are relatively large in diameter, which can replace the role of the bridge pillar in the trench.

Later, the trench filling car was invented, and there are two kinds recorded in the "General Essentials of the Martial Arts", according to the figure, it can be seen that the biggest difference between the trench filling car and the aforementioned trench bridge should be that the protection process for the deployment of bridge personnel is different, and the trench filling car is a vertical bridge plate as a defense, so the personnel can avoid being attacked by arrows and stones when advancing the trench filling vehicle.

The personnel defense of the trench wagons even extended from the front to the sides and roof. However, the load bearing of the opposite deck is much less than that of the moat.

Most of the series of rails, trench cars, etc., that appear later in this article are based on the above prototypes.