The Vitruvian Man

Leonardo da Vinci's 'Vitruvian Man' is said to illustrate the golden ratio. Da Vinci modeled his perfect human form after the proportions laid out by Vitruvius, an ancient Roman architect. The angry-looking man drawn by Da Vinci has reason to smile - he's now considered one of the most recognizable figures on earth.

Geologic Time

IMAGE (Image credit: stock.xchng)Plate tectonics? No sweat. While most of his contemporaries explained inland, mountain-top mollusk fossils as leftovers from the Great Flood, Da Vinci thought otherwise. He supposed (right) that the mountains must once have been coastline before many years of gradually shifting upwards.

The Self-Propelled Car

IMAGE (Image credit: Courtesy of Museo Nazionale della Scienza e della Tecnologia Leonardo da Vinci)It's no Ferrari, but Da Vinci's designs for a self-propelled vehicle were revolutionary for his day. His wooden "car" moved by the interaction of springs with geared wheels. Scientists at one museum in Florence built a replica in 2004 and found it worked as Da Vinci intended.

The Ideal City

IMAGE (Image credit: Courtesy of Museo Nazionale della Scienza e della Tecnologia Leonardo da Vinci)Living in a Milan wrought with plague, Da Vinci envisioned a more efficient city he’d be proud to call home. His architectural draughts are highly detailed and even include horse stables with fresh air vents. To the bewilderment of modern Milanese, he did not make room for a soccer stadium.

The Aerial Screw

IMAGE (Image credit: Courtesy of Museo Nazionale della Scienza e della Tecnologia Leonardo da Vinci)Modern scientists agree it may never have lifted off the ground, but Da Vinci's "helicopter" design is still one of his most famous. The curious contraption was meant to be operated by a four-man team and could have been inspired by a windmill toy popular in Leonardo's time.

The Triple-Barreled Cannon

IMAGE (Image credit: Courtesy of Museo Nazionale della Scienza e della Tecnologia Leonardo da Vinci)More thinker than fighter, Da Vinci's distaste for conflict didn't stop him from dreaming up designs for more efficient cannons like this one. His jacked-up triple-barrel would have been a deadly weapon on the battlefield, fast and light with lots of extra fire power.

The Winged Glider

IMAGE (Image credit: Courtesy of Museo Nazionale della Scienza e della Tecnologia Leonardo da Vinci)Da Vinci's imagination was filled to capacity with ideas for flying machines, including several gliders equipped with flappable wings. This open-shelled model, fitted with seats and gears for the pilot, did not include a design for a crash helmet.

The Revolving Bridge

IMAGE (Image credit: Courtesy of Museo Nazionale della Scienza e della Tecnologia Leonardo da Vinci)Always a fan of the quick getaway, Da Vinci thought his revolving bridge would be best used in warfare. The light yet sturdy materials, affixed to a rolling rope-and-pulley system, allowed an army to pick up and go at a moment's notice.

Scuba Gear

IMAGE (Image credit: By Permission of the British Library Arundel 263, f.24v)Da Vinci's fascination with the sea spurred many designs for aquatic exploration. His diving suit was made of leather, connected to a snorkel made of cane and a bell that floated at the surface. Proving the artist was also practical, the suit included a pouch the diver could urinate in.

Mirror Writing

IMAGE (Image credit: By Permission of the British Library Arundel 263, f.4v,11)Was it a ploy to thwart Renaissance copycats peeking at his notes, or just a way to avoid the inky mess of writing left-handed? Whatever his motives, Da Vinci sure liked mirror writing: most of his journals are scrawled in reverse.