The Rod

The rod and serpent goes back to ancient Greece and a man called Aesculapius who lived around 1256 BC.  He was a doctor of such renown that legend tells that he was able to bring the dead back to life. 

Pluto, the God of the underworld, was so appalled at not gaining the souls of the dead that he complained to Jupiter the head of all Gods. Jupiter obliged by slaying Aesculapius with a thunderbolt - this is the rod.

The Serpent

After his death Aesculapius himself became a god who was worshipped in hundreds of temples.  The temples quickly became places of healing for the sick and were used as the first hospitals. 

Within each one there was a circular pit that contained a species of snake that was harmless, but whose forked tongue was believed to have healing properties - this is the origin of the snake. 
 
Ever since those days the Rod and the Serpent have been used as a symbol of medicine throughout the world.

In Arduis Fidelis

The motto underneath the cap badge can be translated as "Faithful in Adversity".  It sums up the character and the ideals of the soldiers and officers who wear the cap badge, and is just as applicable to all in times of peace as it is in war. 

The need for a steady nerve during periods of pressure can be found in the hospital and the playing field as much as it can be found on the battlefield.