Blight

A Blight refers to a period when darkspawn find and corrupt one of the Old Gods, which is transformed into an archdemon and leads the horde to attack the surface world. The world has seen five Blights to date; as Dragon Age: Origins begins, the fifth Blight has just begun.

The Blight
A Blight is distinct from the occasional darkspawn raids, in which the darkspawn are few, scattered, and disorganized, plaguing only the Deep Roads, underground highway tunnels constructed by the dwarves at the height of their empire. These tunnels—and natural caverns connected to them—extend throughout Ferelden, and possibly elsewhere in Thedas.

When the darkspawn discover one of the Old Gods—ancient draconic creatures slumbering in the depths of the earth—they infect it with their taint, and it rises as an archdemon. Unified by its will, the darkspawn surge up from their tunnels and spread across the surface of the lands, destroying all in their path. Survivors are dragged underground to be eaten or turned into Broodmothers, water sours, crops are spoiled, the land is poisoned and animals sicken. With each passing day, a blight grows. The earth itself withers and dies; the land is leeched of moisture, turning everything dry and brown. The sky fills with rolling, black clouds that block out the sun, making it easier for the darkspawn to surface. As this wasteland spreads, the disease of the blight spreads with it, corrupting all in its path.

The only way to end a Blight is to slay the archdemon, and the only ones who have ever managed such a feat are the Grey Wardens. For this reason, the order holds the respect of most nations, though their presence in Ferelden is the weakest of them all. The chilling thought is that this Blight has begun to spread from Ferelden for precisely that reason.

The Blight Disease
The Blight disease is the corruption spread by the darkspawn. It twists and corrupts all living organisms. Animals and humanoids either go mad and develop physical deformities, or perish from the disease. Surviving humanoids are transformed into ghouls, while surviving animals result in mutations such as bereskarn, blight wolves, and corrupted spiders. In some cases animals (e.g., the mabari dog helped by the Warden in Ostagar) can make a full recovery if given early care; however, most have to be put down to prevent them from spreading the disease further.

Even corrupted animals will eventually be killed by the disease, leaving whole areas completely lifeless.

The Thaw
The Thaw is the period at the ending of a Blight, when the archdemon is defeated and darkspawn are fleeing back into the Deep Roads. When Grey Wardens have defeated the Blight, they often seek out remaining darkspawn in what is called the Thaw Hunt.

The Expansion Pack, Dragon Age Awakening takes place during the Thaw after the Fifth Blight.

The History of Blights in Thedas
The Chantry teaches that it is the hubris of men that brought the darkspawn into Thedas. The mage rulers of the Tevinter Imperium sought to usurp the Golden City — the afterlife created by the Maker for mortals — but were cast out, twisted by their own corruption, only to return as monsters; the first of the darkspawn. The dwarves hold no such beliefs; to them, the darkspawn simply appeared one day and have been their bitter enemies ever since, although it is suggested that some Dwarves (if not all) believe the humans are the reason for their existence.

The First Blight
After the corruption of the magisters, the first darkspawn awaken Dumat, the first among the Old Gods, as the first archdemon. Thedas is nearly overrun; the dwarves come near to extinction, leaving only Orzammar and Kal-Sharok. The first Grey Wardens appear, and Dumat is finally slain at the Battle of the Silent Plains in 992 TE. The Tevinter Imperium is left severely weakened, resulting in a barbarian invasion led by Andraste.
 * Codex entry: The First Blight, Chapter 1
 * Codex entry: The First Blight, Chapter 2
 * Codex entry: The First Blight, Chapter 3
 * Codex entry: The First Blight, Chapter 4

The Second Blight
Zazikel awakens in 1:5 Divine and the second Blight begins, with darkspawn coming out of the mountains in all corners of the continent. They slaughter the entire city of Nordbotten in the Anderfels before the Grey Wardens finally get the word out. The Free Marches and Orlais are hard-pressed to defend themselves, but the Grey Wardens and the armies under Emperor Kordillus Drakon I make the difference. Just over ten years into the second Blight the Orlesians defeat several hordes of darkspawn, including the hard-fought victory at the Battle of Cumberland. As the Orlesians and Grey Wardens share continued victories, the second Blight winds down to its last battle in Starkhaven. Led by the Wardens, the human army destroys Zazikel and the darkspawn are routed for the second time.

The Third Blight
The Old God Toth awakens in 3:10 Towers and the third Blight erupts in the central lands of Thedas with darkspawn coming in greater numbers than ever before. Darkspawn swarm the Tevinter cities of Marnas Pell and Vyrantium as well as the Orlesian cities of Arlesans and Montsimmard. The Grey Wardens in both of these countries are able to quickly organize a defense, and despite heavy losses in the besieged cities, the darkspawn are pushed back. Darkspawn proceed to ravage what is modern-day Nevarra as well the Free Marches, attacking cities along the Minanter River. Pressure from the Grey Wardens in Weisshaupt convinces both the Orlesians and Tevinter to unite, but consent to send aid to the beleaguered city-states. After fifteen years of conflict, the armies of Orlais and Tevinter meet in Hunter Fell and join the Grey Wardens in ending the Blight. Toth is destroyed, and the darkspawn are slaughtered in one of the bloodiest battles in history.

The Fourth Blight
The fourth Blight begins when the archdemon Andoral arises just as the Chantry's exalted march against the Tevinter Imperium ends. This time, the darkspawn appear in great numbers in the northeast and northwestern regions of Thedas. As Antiva is overrun, and its entire ruling family slaughtered, the darkspawn pour into the Free Marches and Rivain. Meanwhile the Blight rises in the Anderfels once again, with the capital city of Hossberg coming under siege. Orlais and the Tevinter Imperium are attacked by fewer numbers and are able to drive the darkspawn back into the depths of the Deep Roads; despite these successes they send next to no aid to the devastated nations.

In 5:20 Exalted the elven hero Garahel leads an army of Grey Wardens and Anders to the city of Hossberg and breaks the siege. With his fellow wardens from Orlais and the Anderfels, Garahel marches to Starkhaven and forms an alliance between the minor kings and teyrns of the Free Marches. Under the banner of the Grey Wardens, this united army marches north, eventually freeing the nation of Antiva from the terror of the darkspawn in the battle of the city of Ayesleigh. It is here where Garahel dies, having personally defeated and slain Andoral in single combat.

So many darkspawn are slaughtered in the fourth Blight that it is considered certain that they will never return. This belief is compounded by rulers choosing to tell the people that the Blight was forever defeated as a way to restore order. Despite the fact that the surface world would not see another Blight for 400 years it is continuously felt underground by the dwarves of Orzammar, a fact that is largely ignored by most except the Grey Wardens.

The Sixth and Seventh Blights
If the parable of the prideful magisters tainting the Golden City is true, and the archdemons are the seven Old Gods of the Tevinter Imperium, it is possible that there are only two more Blights that Thedas will have to endure. What the remaining darkspawn would do once they lack the call of the Old Gods is unpredictable.