|This article describes a concept which is mentioned in J.R.R. Tolkien's works, but was never given a definite name.|
Ulmo's warning was a message given by the Vala Ulmo to Tuor, who was in turn to deliver it to Turgon, King of Gondolin. In the earlier writings it requested that Turgon sally forth to meet Morgoth in open battle, for the Valar would aid their victory, but if he would not go forth to war, then he must abandon Gondolin and lead his people down Sirion and seek back to Valinor.
For the edition of The Silmarillion, Christopher Tolkien and Guy Gavriel Kay rewrote it to adjust it to the late version: Ulmo's warning announced that the doom of Gondolin was coming, suggesting that they seek to find a way to the Blessed Realm. Either way, Turgon did not heed this wise counsel, because of his pride, the love of his beautiful city and Maeglin's advices.
- J.R.R. Tolkien, Christopher Tolkien (ed.), The Book of Lost Tales Part Two, "III. The Fall of Gondolin", pp. 161-162
- J.R.R. Tolkien, Christopher Tolkien (ed.), The Shaping of Middle-earth, "III. The Quenta: [Section] 16", p. 142
- J.R.R. Tolkien, Christopher Tolkien (ed.), The Silmarillion, "Quenta Silmarillion: Of Tuor and the Fall of Gondolin"