Widdershins

Aye, be that as it may, it's clearly intended to exemplify the Alicorns as something special.... then the showmakers forced Miss Faust's creative hand by crippling said Alicorns and reducing them to nothing but mentor figures to tell Protagonists where to go next. 

 But my point remains. A torc is a solid mass of metal. Mostly because it goes around the Chest, not a thin rope around the neck. Proportionally, that thing is as thick around as their legs and about as wide in the center as most ponies' faces. Even if an alloy that merely has gold coloration on the outside, that is still an absurd amount of metal to heave around. By estimation of proportion that is at least Six Pounds of metal around your neck vertebrae heaved up by the royal necks for most of the day.

 That sure as heck can stop most arrows and low caliber bullets, I imagine! The Queens of Equestria got some muscle to them! That's technically, as I see it, the equitable action of carting around a Prizewinner Wrestling Belt around everywhere you go! 

 Oh and, one could say Earth Ponies have the magical ability of "Landwalking" wherever there is the element of Earth, they can walk upon it with ease. But somehow that isn't magical enough for some!

what if it's just a shell? and it's hollow on the inside?

@Lord Valtasar

And sealed inside it they keep a horde of maddened magical wasps so if anyone tries to attack them they can break it open and engulf the would-be assassin in insectoid agony! Or maybe they keep the last surviving snippets of Starswirl's original Beard of Power. Or maybe they contain all (formerly) known samples of the material that Chrysalis' throne was made out of because material that permits magic nullification is simply too dangerous to be let out of their presence, also explaining the apparent uselessness of the princesses, their guards, their nobility, basically anyone who tries to do anything useful in Canterlot, and every villain who ever kidnapped the princesses. The possibilities are endless!