The final season of Game of Thrones has finally arrived, and with it has come the White Walkers' long-awaited invasion of Westeros. The conflict is unlike anything the series’ protagonists have ever faced, but when compared against the continent's history, the circumstances are hardly unprecedented. The White Walkers - known as the Others in the A Song of Ice and Fire books - also marched on Westeros during a legendary time period known as the “Long Night,” long before the construction of the Wall and the founding of the Night’s Watch.
The Long Night doesn’t just precede the Wall and its guard, the Night’s Watch - it’s the reason both of those things exist. The Long Night was an era of darkness that nearly snuffed out humanity once and for all, and its impact was felt for millennia thereafter.
The Long Night, an unprecedented event that nearly decimated Westerosi civilization, was preceded by something equally rare: a sustained period of peace. After the First Men crossed the Narrow Sea and began to colonize Westeros—thousands of years before the events of Game of Thrones—they came into conflict with the Children of the Forest.
After generations of warfare, a peace conference was called on a Westerosi island, resulting in an agreement that became known as “The Pact.” The leaders of both races carved faces on all the island's weirwood trees—providing the location's name, “The Isle of Faces”—so the Old Gods could witness the agreement. An idyllic period of peace followed for several generations, but it was not to last.
Following the Pact between the First Men and the Children of the Forest, a new era began in Westeros known as the Age of Heroes. This legendary period saw several of the continent’s major houses founded by semi-mythical figures, such as Bran the Builder and Lann the Clever.
Eventually, the Age of Heroes would transform into Game of Thrones's contemporary age, particularly after a second wave of Andal invaders hit the shores a few thousand years later. Prior to that event, however, the Age of Heroes was interrupted - and nearly ended - by the Long Night.
If the historical timeline established in A Song of Ice and Fire is to be believed, the Long Night occurred some 8,000 years before the events of Game of Thrones, though there’s significant reason to doubt those numbers. Even in-universe characters can’t seem to agree, with most maesters at the Oldtown Citadel believing that the Long Night was probably closer to 6,000 years ago. Some amateur historians date it even more recently.
The events of the Age of Heroes and the Long Night occurred so long before Jon Snow and Daenerys Targaryen walked the earth, separating fact from fiction becomes a gargantuan task - knowing how much of Westerosi history has been mythologized and embellished seems truly impossible.
When the White Walkers first appear in Game of Thrones, they’re regarded as a somewhat mythical threat that the vast majority of Westeros disregards; however, this was hardly their first appearance on Westerosi ground. The Long Night was not only the first time the White Walkers were mentioned in history books - it was also the first and only time they invaded Westeros until the events of Game of Thrones’s final season.
The White Walkers - known as the Others in George R. R. Martin's books - appeared without warning at the beginning of the Long Night and began their slow march on Westeros, aided by their legions of undead wights. As the Long Night predated the construction of the Wall, the invasion was much more straightforward than their contemporary efforts - before long, they managed to put the entire continent on the brink of extinction.