The Battle of the Blackwood Bridge occurred between General Tytugg's goblins and Mother Muleclaw the Second's shrykes during the Third Great Migration and led to the destruction of both these forces in Undertown.
Cause of the Battle
When the Librarians learnt of the manic plan of Vox Verlix to instigate the Dark Maelstrom and destroy Undertown, they grasped the opportunity by which to ensnare two of their greatest foes and escape unimpeded with the innocent Undertowners towards the Deepwoods in search of a new beginning in the Free Glades.
To do this, the Librarians carried out their plan to coax both the goblins and shrykes into the Great Storm Chamber Library in the Sewers beneath Undertown at the time of the eleventh hour - when the Dark Maelstrom would strike. Firstly, Rook Barkwater traveled to the Court of the Shryke Sisterhood, under the pretense that he was an exiled Librarian willing to sell to the shrykes information in return for a path to the Deepwoods. He told the Mother Muleclaw the Second of how the goblins had gained access to the sewers via a secret entrance, and how, with the knowledge of entry to the sewers, the shrykes would be able to gorge upon both goblins and librarians alike. Previously Vox Verlix had told a similar story to Tytugg's goblins.
The Eleventh Hour
At the eleventh hour the goblins entered the sewers via the great Eastern Entrance, and were surprised to find it unguarded. Simultaneously, the shrykes entered the sewers through sewage pipes which ran into the Edgewater River on the west wall of Undertown. They met in the Great Storm Chamber Library.
On the Blackwood Bridge
With both goblins and shrykes shocked by the absence of the Librarians, the two armies engaged on the Blackwood Bridge in the Great Storm Chamber Library. Many on both sides fell whilst, simultaneously, the Dark Maelstrom struck and the water level in the Library began to rise rapidly. However, it was not through drowning that the forces were killed, but by rock demons, who, upon finding such promise of a huge meal, fell upon both shrykes and goblins and devoured them.