Reyne Rebellion

"When our vassals, the Reynes of Castamere, dared to rise up against the Lannisters, they learned how dangerous it can be to taunt a lion. I, Tywin Lannister, led the assault on Castamere to put down this rebellion. I made an example of them, to anyone who doubts our might."

- Tywin Lannister

The Reyne Rebellion was an uprising which occurred in the Westerlands, when House Reyne of Castamere tried to rise against House Lannister of Casterly Rock. House Reyne perceived that their Lannister overlords were weak, due to the incompetent leadership of the House's current head, Tytos Lannister, the Lord of Casterly Rock and Lord Paramount of the Westerlands. The sigil of House Reyne was also a lion, but a red one instead of the golden lion used as the sigil of House Lannister. The rebellion of the Reynes against the Lannisters was thus symbolically seen as a clash of lions.

Background
The rebellion occurred around the time Cersei Lannister was a little girl, as she remembers when her father crushed the rebellion.

Tytos's son, the young Tywin Lannister, led his House's armies to crush the revolt. Unlike his father, Tywin was ruthless and cunning, and soon he defeated the Reynes and burned Castamere to the ground. Tywin put all surviving Reynes to the sword, man, woman, and child, to make an example of them for any Lannister vassals who would dare challenge their dominance again. Tywin subsequently had the corpses of the executed Reynes hung from the gates of Casterly Rock on public display, where he left them to rot for the entire summer (it was a long summer, which lasted many years).

The extinction of House Reyne marked the first major step in the return to glory of House Lannister, in which Tywin almost singlehandedly rebuilt the fortunes and strength of his House.

Tywin's victory was immortalized by the minstrels in the popular song, The Rains of Castamere.

Season 3
Queen Cersei Lannister tells Margaery Tyrell about the origin of the song, The Rains of Castamere, just before the wedding of her brother Tyrion to Sansa Stark, in order to threaten her. Cersei recounts the rebellion of the Reynes of Castamere, and how her father ultimately crushed their rebellion and executed any survivors down to the last child. Cersei warns Margaery that in their time the Reynes were the second wealthiest family in Westeros, behind House Lannister, but no one is content with being the second most powerful. Cersei bluntly notes that House Tyrell is the second wealthiest family in Westeros now, implying that the Tyrells should learn from the example the Lannisters made of the Reynes and keep their ambitions in check.

In the books
In the A Song of Ice and Fire novels there were two major Houses of the Westerlands that joined together to rise in rebellion against the Lannisters: House Reyne of Castamere, one of the richest Houses in the Westerlands, and House Tarbeck of Tarbeck Hall, an ancient line dating back to the time of the First Men. Lord Roger Reyne, called "the Red Lion of Castamere", and Lady Ellyn Tarbeck, née Reyne, who had already defied Lord Tytos on a previous occasion, led the rebellion but were crushed by the young Tywin, who eliminated their entire families. Lady Ellyn had been borne a Reyne, and previously married into House Lannister but bore no children, before later remarrying into House Tarbeck. Tywin's victory and ruthlessness earned the attention of King Aerys II Targaryen, and within a few years he appointed Tywin as Hand of the King, a position he would serve in for twenty years.

The revolt doesn't have a formal name in the books.

Some of the details which Cersei provides in "Second Sons" contradict information from the novels. In the TV series, Cersei says that the Reynes rebelled against her father Tywin; loosely speaking this is true, but Tywin's father Tytos Lannister was still alive and it was he who they were rebelling against, though it was Tywin who put down the rebellion as his son and heir. More importantly, the rebellion occurred when Tywin was very young, indeed it was seen as quite impressive that such a young man performed so well in war (ironically, somewhat like the future Robb Stark). Tywin possibly wasn't even married yet, however, and Cersei certainly had not been born. The simple numbers don't match well: Tywin was appointed as Hand of the King soon after he put down the rebellion, and served in that position for twenty years. Tywin resigned a few years before Robert's Rebellion broke out, then another fifteen years passed before the War of the Five Kings (seventeen in the TV series). Thus the Reyne Rebellion had to have occurred roughly forty years before the War of the Five Kings, which would require Cersei to be at least ten years older than she actually is in order to remember it. Cersei in the books and actress Lena Headey are both in their mid-thirties when the story begins, but Cersei would have to be at least in her mid-forties to remember the rebellion of House Reyne. Moreover, while the Reynes were certainly fairly rich, they were not the second richest family in all of Westeros.