A drawbridge is a type of mobile bridge that can be raised with the help of a mechanical installation to allow entry through a gate, or to allow maritime traffic across a body of water.

The moving part is very wide and rotates through an axis "Axis (mechanical)") horizontally") or as a hinge. To raise the platform, ropes or chains attached to the corners opposite the axis are used.

To secure entry into a city, a fortress or castle, these types of mechanisms and methods were used in the Middle Ages. continuing its use in the Modern Age.

The entrances to forts and castles were always a weak point, so throughout history different devices were devised for their protection. With the help of a drawbridge, access through the moat could be avoided effectively and quickly. In the Middle Ages, destructible wooden bridges were also used if necessary, but a drawbridge, in addition to its flexibility, also allowed a quick exit if necessary. To prevent the bridge from being lowered by hooks from the outside, the platform was often housed in a slot.

In the Middle Ages, two types of constructions were mainly used to raise the platform:

Both systems do not effectively solve the problem due to the different moment of forces necessary to lift the bridge: greater when the bridge is stretched, lesser as it is raised until the portal is closed. There were two main systems used to resolve this issue.

This type of bridges are also used for access over bodies of water. Bridges with two platforms are mainly used and each one rises in opposite directions and are usually based on the roller principle.