They beat me hot but it's cold that I'm the hardest, It is of my help that one builds because it is of my solidity of which one is sure, Quadrupeds when I dart, biped when I prick, I am as lively as silver, but always of marble, Worn I protect, or...

They beat me hot but it's cold that I'm the hardest,It is of my help that one builds because it is of my solidity of which one is sure,Quadrupeds when I dart, biped when I prick,I am as lively as silver, but always of marble,Worn I protect, or for others I bring happiness,Tamed, the stallion that carries me dreams yet to be elsewhere,
Who am I ?