Battle at Long Lake

The Battle at Long Lake was a military engagement fought approximately 75 years before the events of Game of Thrones.

Background
United by a new King-Beyond-the-Wall named Raymun Redbeard, the Free Folk (known derisively as "wildlings") launched a major attack into the Seven Kingdoms south of The Wall.

The numbers of the Night's Watch, which guarded the Wall, had drastically diminished since the Targaryen Conquest nearly two centuries before. The Watch used to have a steady stream of recruits from the losing sides in the endless wars between the independent Seven Kingdoms, but after the Targaryens united the kingdoms and put an end to the internal wars, the stream of recruits fell to only a trickle. As a result several of the 19 fortresses of the Watch used as bases for patrols had to be abandoned - even their original headquarters The Nightfort, the first castle along the Wall.

Raymun realized that the Watch's dwindling patrols were now spread very thin, with miles-long stretches of the Wall which were not patrolled at all for days. Therefore he sent climbers on the difficult ascent up the Wall - unnoticed and unimpeded by any fire from defenders above. The climbers then dropped ropes down which the rest of Raymun's wildling horde used to mount the Wall, then pass down to the southern side.

The Night's Watch didn't even notice that the entire wildling horde had crossed over the Wall. Raymun proceeded to lead his army south through the Gift and then into the North itself, whose lands and homesteads were taken completely by surprise.

Battle
Eventually the head of House Stark, as Warden of the North, led out his armies to stop the wildling advance. Along with the immediate forces raised from the Starks' own lands, they were joined by the forces of their vassals House Umber - famed warriors whose lands are located closest to the Wall, making them bitter enemies of the wildlings.

The Starks and Umbers attacked Raymun's hosts at the shores of Long Lake. The wildling army was destroyed and Raymun himself was killed.

Aftermath
Raymun Redbeard's assault was the last major attempt by a King-Beyond-the-Wall for almost a century, until Mance Rayder united the wildlings again as the new King-Beyond-the-Wall.