When passing through Moria, the members of the Fellowship of the Ring found themselves in the Chamber of Mazarbul, not far from the Balin’s tomb. There was a trap. They were attacked by the cave trolls, the orcs of Moria, and the Uruk-hai of Mordor. A troll was injured when trying to get through a solid door made of stone. It did not open completely, so the attackers jostled, preventing each other from squeezing into it. They received a serious rebuff. Some of the attackers were killed, the rest had to retreat to the corridor.
When the members decided to use the eastern exit to escape, a huge orc, a leader, entered and threw a spear at Baggins. It touched the mithril mail without harming Frodo. The leader was killed by Ark, who took Frodo and rushed into the corridor with others. At that moment, a balrog of Moria approached, and Gandalf brought down the ceiling of the Chamber.