Fall of Mount Gundabad
From Tolkien Gateway
The First Sack of Gundabad, took place in the mid Second Age. It was a conflict in which Orcs invaded Mount Gundabad, and drove the Dwarves of Durin's folk from their holy site. One which they would not gain back till after the War of the Ring.
References
- The Peoples of Middle-Earth, Of Dwarves and Men, page 305