Fort Dragonfall

Fort Dragonfall is a fortress that is found at Nohr in Fire Emblem: Fates

History
Prior to the events of Fates, an elder dragon died in this location. Thousands of years later, an architect decided to construct a fortress here utilizing the dragon's bones.

The fort was then used by Nohrian soldiers, although it was seemingly abandoned after an unknown period of time.

Birthright
Fort Dragonfall makes its first appearance during Chapter 20, where the Hoshidan army decides to go through to reach Windmire faster and hide from Nohrian forces searching for them.

Ryoma notes that the fortress is unusually empty like all the other places in Nohr they visited, and suspects that it may be a trap. Iago teleports inside the fortress, still observing the Avatar's progress through Nohr. He collapses the entrance they entered through and tells them that Garon gave him new magic powers to use on them. Iago uses his powers to revive the dragon, which results in the fortress' walls becoming much more stronger. Stomach acid begins to form inside the dragon, and Iago summons a horde of Faceless to kill them quicker.

After the Faceless' leader is killed, Azura sings to undo Iago's spell, which allows the Hoshidans to break out of the walls and escape.