Siege of Angband
The Siege of Angband was the 400-year leaguer of the Noldor around the fortress of Morgoth in the early centuries of the First Age, which began following the Dagor Aglareb. The Noldor and their allies possessed insufficient force to assault Angband directly. Fingolfin and Fingon kept watch from Hithlum, Finrod and then Orodreth from Tol Sirion, Angrod and Aegnor from Dorthonion, and the Sons of Fëanor watched the east.
It was during the Siege that Turgon's people left Nevrast to build Gondolin. Other Elven cities, Brithombar and Eglarest were also established by the Sindar on Falas, and Nargothrond, the realm of Finrod. The siege was incomplete, as Morgoth was still capable of sending out various forces of orcs to harass the elves, such as the attack of Hithlum; but the Noldor were grown strong enough, that these task forces posed no significant threat.
After about four hundred years, the Siege was broken in the Dagor Bragollach.