Leonardo da Vinci told the Duke of Milan that he could build a portable bridge.
The claim appeared in Leonardo’s famous 1482 letter to Ludovico Sforza, in which he presented himself as an engineer, architect, inventor, and military designer. Alongside weapons and fortifications, Leonardo described bridges that could be assembled quickly, moved easily, and used by armies to cross rivers or escape danger. The practical promise helped him attract Sforza’s patronage in Milan.
Leonardo’s surviving notebooks contain several bridge designs. Some were intended for rapid military construction, while others used interlocking wooden beams to create self-supporting structures without nails, ropes, or dowels. These designs show how Renaissance engineering combined geometry, materials knowledge, and military needs.
The bridge was a proposal rather than a documented portable structure that Leonardo built for the duke. Another famous Leonardo bridge design was created later for Sultan Bayezid II: a proposed single-span crossing of Istanbul’s Golden Horn. That project was never constructed, but it illustrates why “bridge” is the canonical answer to this question.