It has taken more than 500 years to get from the drawing board to the showroom, but today the first working model of the "car" conceived by Leonardo da Vinci is to go on display at an exhibition in Florence.
Eight months' work by computer designers, engineers and joiners has proved something that had been doubted for centuries: the machine sketched by history's most versatile genius in or around 1478 actually moves.
"It was - or is - the world's first self-propelled vehicle," said Paolo Galluzzi, director of the Institute and Museum of the History of Science in Florence, who oversaw the project.
Perhaps sensibly, humanity waited for the invention of steam power and then the internal combustion engine. Leonardo's car, 1.68m long and 1.49m wide (5ft 6ins by 4ft 11ins), runs on clockwork. The springs are wound up by rotating the wheels in the opposite direction to the one in which it is meant to go.
"It is a very powerful machine," Professor Galluzzi said. So powerful that although they have made a full-scale "production model", they have not dared test it. "It could run into something and do serious damage," he said.
The vehicle demonstrated in Florence yesterday was a one-third scale replica.
Several attempts were made in the last century to construct the vehicle. None worked.
They were vitiated by a misunderstanding: that Leonardo powered his vehicle with the two big leaf springs, shaped like the arms of a crossbow, shown in his sketch on folio 812r of the Atlantic Codex, one of the great collections of his studies and sketches.
In 1975 Carlo Pedretti, director of the Armand Hammer Centre for Leonardo Studies in Los Angeles, published a paper showing early 15th century copies in the Uffizi archives of some early Da Vinci sketches. "Two of the drawings represent a view from above of the spring mechanism of the well-known self-propelled vehicle in the Atlantic Codex," he wrote.
Studying the copies, Prof Pedretti realised that the springs were not meant to drive the car but to regulate a drive mechanism located elsewhere. In 1996 his intuition was reported in a book by an American robotics expert, Mark Rosheim.
"He believes that motive power is provided by coiled springs inside the tambours", Mr Rosheim wrote.
The theory that the car's "engines" were sited in a couple of drum-like casings on the underside resolved many of the enigmas in Leonardo's design. But until Prof Galluzzi and his team got to work, it was still just a theory.
Their first step was to create a digital model by computer aided design.
"That took four months," Prof Galluzzi told the Guardian. "But at the end we had a machine which we knew ought to work."
To test Leonardo's genius to the limit it was decided to try to realise his vision with materials available to the craftsmen of his time. That meant mainly wood.
Florentine furniture restorers were asked which types their predecessors would have chosen for which parts of the vehicle.
"The biggest problem was to find a wood for the cogs, because that had to be hard and resistant.
The finished vehicle contains five sorts of wood and "mechanisms of extraordinary refinement".
Leonardo scholars have long believed the car was intended to provide special effects in some kind of performance.
It has a brake that can be released at distance by an operator with a hidden rope, so it would have appeared to start by itself.
A programmable steering mechanism allows it go straight, or turn at pre-set angles. But only to the right. Good in towns like today's Florence, with a one-way system. As ever, Leonardo was centuries ahead of his time.