Fictional time period from J. R. R. Tolkien's universe of Middle-earth.
Ages: First Age - Second Age - Third Age
The Second Age began with the final overthrow of Morgoth by the combined armies of Valinor and the Three Houses of Men.
It lasted for 3441 years, and ended with the downfall of Sauron, when he was defeated by the Last Alliance of Elves and Men following the downfall of Númenor.
This age was characterized by the rise (to insolence, eventually) of Númenor, the rise of Sauron in Middle-earth, and the early wars of the Rings between the Sauron and the Elves.