Battle of FornostBattle of Fornost (1975 T.A.) - After Angmar conquered Arthedain, Gonder came to the aid (albeit too late) of their brethren.

 

"Then Cirdan summoned all who would come to him, from Lindon or Arnor, and when all was ready the host crossed the Lune and marched north to challenge the Witch-king of Angmar.  He was now dwelling, it is said, in Fornost, which he had filled with evil folk, usurping the house and rule of the kings.  In his pride he did not await the onset of his enemies in his stronghold, but went out to meet them, thinking to sweep them, as others before, into the Lune.

 

"But the host of the West came down on him out of the Hills of Evendim, and there was a great battle on the plain between Nenuial and the North Downs.  The forces of Angmar were already giving way and retreating towards Fornost when the main body of the horsemen that had passed round the hills came down from the north and scattered them in a great rout.  Then the Witch-king, with all that he could gather from the wreck, fled northwards, seeking his own land of Angmar.  Before he could gain the shelter of Carn Dûm the cavalry of Gondor overtook him with Eärnur riding at their head.  At the same time a force under Glorfindel the Elf-lord came up out of Rivendell.  Then so utterly was Angmar defeated that not a man nor an orc of that realm remained west of the Mountains." ~The Return of the King (Appendix A)