Undead city blocked path

How do I get passed the boulders in the Undead City?

Look around the undead city, there is a hammer, equip it and use it to smach the rocks

I picked up the dark mail in the undead city, but when I smash the rocks I get the message my weapon is not strong enough. Any other ideas?

You can smash those rocks only if you got the maul and the quest for it too. You can get this quest from a lady in a house down there in the Undead City. Look around, check all doors, mostly at the eastern part of the map. : )