The Summer Sickness

The Summer Sickness was a terrible plague which wracked Westeros during the fortieth decade of the third century. Many thousands perished, including King Rhaegar I Targaryen.

Background
The plague is largely thought to have come up from the Summer Islands by way of Oldtown, from there spreading throughout the Reach and the rest of the Seven Kingdoms.

The Sickness
Only the North and the Iron Islands fully escaped the ravages of the disease, for it seemed to falter in the more inhospitable climes. Many took this as further proof that the illness had been sent by the gods - in the eyes of the Faithful, as punishment for their sins; in the eyes of the Ironborn, as punishment for their blasphemy; and in the eyes of the Northmen, opinions were divided.

Whatever the case, the plague spread too quickly for many to stop, though massacres and embargoes would attempt it. Dorne at once closed her gates, but the sickness had already passed through the passes - spreading through the lands of the Stony and Sandy Dornish folk, but scarcely touching those along the eastern coasts.

In the Vale, an armed party of commonfolk were put down at the Bloody Gate, which was sealed against all comers as the word of the sickness spread. All the same, Gulltown proved the entryway for the plague, merchants from King's Landing unwittingly bringing the disease and spreading it thence. The Vale was, all the same, not near so heavily affected as other regions.

The Plague Wanes
Over time, the plague began to burn itself out, the efforts of maesters doing much to help to stem the tide. By 345AC, just over five years after the first initial case was sighted, the disease was all but disappeared from the major population centers and settlements, pervading only in out-of-the-way areas and forgotten parts of the countryside.

Major Casualties
Many thousands fell to the Summer Sickness, though some knew its grip more personally than others. Some of the major figures to fall to the illness include;
 * King Rhaegar I Targaryen

Legacy
The plague struck fear into many during its reign, a fear that was not truly alleviated until the Mead Summer and the return of both peace and plenty.

The losses incurred, and the general state of anxiety, suspicion, and paranoia, caused many to turn to the Faith in this time of trouble. With Oldtown being the initial seat of the disease and one of the most heavily hit locations early on, the power of the Faith grew greatly in the city, sowing the seeds for the power of the Starry Septon by the time of the Southern Schism.