An all-too-common mistake that tanks make.

[Sapphidia]

No, you cannot. It is very easy to test, and you can not block/parry attacks from behind you. Attack a mob, and turn your back to it. You're not going to block/parry.

I don't know where you got your information, but I'm sorry to tell you that it is wrong.

Read up for my edit ^^ You CAN block special attacks, it's only basic auto attacks that you can't block/parry from behind. Of course, on mob packs this is most of the damage as you can usually just step out of the special ones, but it explains why people assume you can block from behind.

I think it's to do with how the game models AOE. Once it detects you're in an AOE area for a move, it doesnt bother to check your facing in relation to a mob, so if the move is physical and blockable it'll do a block check. Easy mob to test this on is the 48 Natalan Watchwolves east of Camp Dragonhead. Aggro one, turn your back. They'll hit you with every auto attack (you'll see some Dodges of course), but if they do their Neck Rip ability you'll be able to block/parry it.