Archimedes was a military engineer who made practical inventions that helped the Syracusans to end a three-year siege (214-212 BC) by the Romans by;
1) He invented a way through which the Roman ships could catch fire by focussing and reflecting sunlight on their sails by use o a giant mirror.
2) As a military engineer on the payroll of the king, he built the Claw of Archimedes that hooked the Roman ships out of the water and flipped them over.
Through these inventions and fire from ballistas and onagers mounted on the walls of the city, the Romans were frustrated and forced them to use costly direct assaults