Gothic design also introduced the drawbridge, which consisted of a wooden platforms suspended by chains to cross-beams. The principle used to construct these designs was similar to the functioning principles of a see-saw. When lowered, the bridge created a passage across the moat. The bridge was raised by depressing the inner ends of the lever-beams, which then pivoted, thus bringing the platform up vertically against the front of the building. The design of this drawbridge system created an outer door, creating another barrier for attacking parties who either had to batter it in or to bring down by cutting the chains.
Drawbridges were more effectual and dependable when compared to the previously used portable bridges. An example of a draw-bridge can be seen at Aigues-Mortes in France. A pointed arch was also used in the design of this doorway, a structure distinct in this building design. By the 15th century drawbridges were universally used in fortress and castle construction. Gothic architects also designed constructs to defend the rivers that flowed through fortified towns and castle fortresses. River arches were guarded by gratings or iron portcullises.
The history of bridges date back to the time of the Romans, as does all other architectural structures seen in the Gothic era. Romans used arches under their bridge structure as a form of decoration and glorification. In Gothic design, these arches were transformed into defense mechanisms to protect the passage across rivers and to protect the fortresses they flowed through. Bridges were of great importance in the middle ages because they served as public highways and military outworks.