As an engineer, Leonardo conceived ideas vastly ahead of his own time, conceptualizing a helicopter, a tank, concentrated solar power, a calculator, and the double hull, and outlining a rudimentary theory of plate tectonics. Relatively few of his designs were constructed or even feasible during his lifetime, but some of his smaller inventions, such as an automated bobbin winder and a machine for testing the tensile strength of wire, entered the world of manufacturing unheralded. As a scientist, he greatly advanced the state of knowledge in the fields of anatomy, civil engineering, optics, and hydrodynamics.

For more information:
http://en.wikipedia.org/wiki/Leonardo_da_Vinci
Other Da Vinci's Inventions
Da Vinci's Mysterious Inventions

Machine for Storming Walls

Ornithopter Flying Machine

Eight Barreled Machine Gun

Automatic Igniting Device for Firearms

Parachute

Stretching Device for a Barrel Spring

Giant Crossbow

Flying Machine

Design for a Boat

Artillery Park

Armored Car

Archimedes of Syracuse (c.287 BC - c. 212 BC) was an ancient Greek mathematician, physicist and engineer. Although little is known about his life, he is regarded as one of the most important scientists in classical antiquity. In addition to making important discoveries in the field of mathematics and geometry, he is credited with producing machines that were well ahead of their time.

For more information:
About Archimedes
Archimedes Palimpsest

Burning Mirror

Archimedes Principle

Archimedes Screw