Henneth Annûn built
Event Type: Military/Strategic
Age: 3rd Age - The Stewards
2901 Most of the remaining inhabitants of Ithilien desert it owing to the attacks of Uruks of Mordor. The secret refuge of Henneth Annûn is built.
The Return of the King, LoTR Appendix B, The Tale of Years: The Third Age
It was [Túrin II] that built secret refuges for his soldiers in Ithilien, of which Henneth Annûn was the longest guarded and manned.
The Return of the King, LoTR Appendix A, Annals of the Kings and Rulers: Gondor and the Heirs of Anárion: The Stewards
Túrin II […] In his time […] But Gondor makes and keeps up secret strongholds there, especially in North Ithilien. The ancient refuge of Henneth Annûn is rebuilt and hidden. The isle of Cair Andros in Anduin is fortified.
The Peoples of Middle-Earth, HoME Vol 12, Part 1, Ch 7, The Heirs of Elendil: The Ruling Stewards of Gondor