- "Aegon V tried to hatch stone dragon eggs with sorcery and burned to death."
Summerhall was a lightly fortified palace that served as the summer residence of House Targaryen. It was destroyed by a fire that killed King Aegon V as well as his heir. Rumor suggests that the tragedy began with an attempt to hatch ancient dragon eggs.
In the books
In the A Song of Ice and Fire novels, the Tragedy at Summerhall is a terrible event still fresh in the memory of the people of Westeros. While what exactly transpired has yet to be described in detail, fans have put together a vague outline of the tragedy by piecing together bits of information.
From a young age, Aegon V Targaryen was fascinated with the possibility of hatching dragon eggs and bringing dragons back into the world. Aegon and his brothers Aerion and Aemon each possessed a dragon egg, his having been placed in his crib when he was a baby. As he grew older, this fascination grew into an obsession. It was not helped by Aegon's growing belief as the nobility resisted more and more of the reforms he was trying to implement to improve the lives of the smallfolk that, if he had dragons at his command, he would have the power he needed to force the nobility to comply with his wishes.
Years later, Aegon's son Prince Duncan Targaryen gave up his crown and married Jenny of Oldstones. Jenny was friendly with a woods witch whom she believed to be one of the Children of the Forest. This woods witch predicted that the Prince That Was Promised would be born to Aegon's grandchildren, Aerys and Rhaella. This led to their father Jaehaerys II arranging Aerys and Rhaella's unhappy marriage.
In 259 AC, Aegon attempted to hatch the dragon eggs at Summerhall. The attempt went horribly wrong and a great fire broke out. All within were killed, including Aegon and his son Duncan. Ser Duncan the Tall, Lord Commander of the Kingsguard, Aegon's close friend since childhood and Duncan's namesake, was also killed in the fire. This is evidenced by the fact that Kingsguard members serve for life and Ser Gerold Hightower was Lord Commander when Ser Barristan Selmy joined the following year.
It has been implied that the Tragedy at Summerhall was no accident. Having married for love himself, Aegon permitted his sons to do the same, although this was not politically wise and made him enemies within the Seven Kingdoms. Barristan states that this led to treason and turmoil, ending at Summerhall in sorcery, fire, and grief.
The fate of the dragon eggs has never been stated, though the were likely destroyed when the ceiling collapsed.
The deaths that occurred at Summerhall were mourned throughout the realm. The song about Duncan and Jenny's love includes a lyric about her dancing with ghosts, suggesting that the grief brought about by Duncan's death drove Jenny to madness. Jaehaerys took the throne, but was heavily traumatized by the deaths of his father and older brother. He ruled for three years before dying prematurely. His son Aerys succeeded him.
Rhaegar Targaryen was born on the same day that the tragedy took place. In his parents' eyes, the tragedy at Summerhall either heralded or directly contributed to Rhaegar's birth. He grew up having a complex fascination with Summerhall. He believed himself to The Prince That Was Promised, having been "born amidst smoke and salt". Here he was happiest, yet also saddened by the memory of the tragedy. He liked to visit by himself and sleep in the ruined hall of Summerhall beneath the moon and the stars. He would bring his harp on these visits and sing of the death of kings.
Certain details about the event are mentioned in the books. Ser Alester Florent mentions it to Ser Davos Seaworth as example of an attempt to wake dragons leading to tragedy. Barristan Selmy tells Daenerys Targaryen in detail about the events that lead to the tragedy and Rhaegar's fascination with the ruined castle. While traveling through the Riverlands, Arya Stark and the Brotherhood Without Banners visit the Ghost of High Heart to hear the future and learn the whereabouts of Lord Beric Dondarrion. Old, stooped and very short, she is clearly the woods witch who befriended Jenny of Oldstones, despite Barristan's belief that she died at Summerhall. This evidenced by her telling Arya "I gorged on grief at Summerhall" and asking that Tom O' Sevens sing her "my Jenny's song". She also predicts the death of King Renly Baratheon as well as the Red Wedding and the Purple Wedding.
George R.R. Martin has stated that he intends to write more of the Tales of Dunk and Egg, eventually covering the entire lives of the two characters. Since both of them die in the Tragedy at Summerhall, it may make a direct appearance in the final novella.