Tirion

According to the Annals of Aman in volume X of The History of Middle-earth, the building of Tirion was begun in the Valian Year 1133, and completed in 1140. Translating Valian Years into conventional solar years, that means that Tirion was started some 3,469 years before the Darkening of Valinor, and took about 67 years to complete.

We have no specific account of the city's destruction, but it should be noted that Ar-Pharazôn's forces were apparently encamped around the city when they were buried under falling hills. This may be taken to imply that Tirion was also buried at the time of the Downfall of Númenor in II 3319, though this is nowhere stated explicitly.

The name Tirion goes back to the earliest of Tolkien's tales, and originally seems to have meant simply 'watchtower' (being a reference to a single building in those early stories, rather than an entire city). In his Appendix to The Silmarillion, Christopher Tolkien associates the name with the element tir-, meaning 'watch', presumably in reference to its location watching the only pass in the Mountains of Defence.

In his notes on the poem "A Elbereth Gilthoniel" in The Road Goes Ever On, Tolkien mentions in passing that Tirion is interpreted 'great watch-tower', thus giving us a direct translation.