The Great Council of 101 AC

When Prince Baelon, heir to old King Jaehaerys, died before his father, the succession stood in doubt, and rather than decide it himself the Conciliator summoned the first Great Council in the realm's history. The lords of Westeros descended upon Harrenhal in such numbers that half a year was spent in the choosing. Fourteen claims were heard, but in truth the matter lay between two: Laenor Velaryon, grandson of the king's eldest son through his daughter Rhaenys, the Queen Who Never Was; and Prince Viserys, son of Baelon, heir male of the male line. The lords chose Viserys, it is said by twenty voices to one, and in that choice set down an iron precedent: the Iron Throne does not pass to a woman, nor through a woman to her sons. Half a century later, that precedent would be the battle-cry of the greens, and the realm would bleed for it in the Dance of the Dragons.