Ruin of the Havens of the Falas
Event Type: Military/Strategic
Age: 1st Age
Date: October 1, 0473
But in the next year, ere the winter was come, Morgoth sent great strength over Hithlum and Nevrast, and they came down the rivers Brithon and Nenning and ravaged all the Falas, and besieged the walls of Brithombar and Eglarest. Smiths and miners and makers of fire they brought with them, and they set up great engines; and valiantly though they were resisted they broke the walls at last. Then the Havens were laid in ruin, and the tower of Barad Nimras cast down; and the most part of Círdan's people were slain or enslaved. But some went aboard ship and escaped by sea....
The Silmarillion, Quenta Silmarillion, Ch 20, Of The Fifth Battle: Nirnaeth Arnoediad
The exact date is not known, but a date is used to keep chronological order, and to show the known season.