Tully-Arryn alliance

The Tully-Arryn alliance was sealed in a double wedding ceremony at Riverrun fifteen years before the events of the book. Eddard Stark and Jon Arryn, who had been fostered together as boys in the Eyrie, stood side by side in the sept at Riverrun to wed two sisters, the daughters of Lord Hoster Tully. Ned married Catelyn, while Jon Arryn married her younger sister Lysa. This marriage bound the Lord of the Eyrie and Hand of the King to the Tullys of Riverrun, creating a political and familial link between the Vale and the riverlands that would have profound consequences for the realm.

The Alliance as a Political Instrument

When Jon Arryn died suddenly, Catelyn immediately suspected the Lannisters. She received a secret letter from Lysa, written in a private language they had devised as girls, warning that the Lannisters had murdered the Hand. The letter was concealed inside a carved wooden box containing a Myrish lens, delivered to Maester Luwin at Winterfell. Catelyn read the message and burned it, then urged Ned to accept Robert Baratheon's offer to become the new Hand of the King so he could investigate the murder. "Now we truly have no choice," she told him. "You must be Robert's Hand. You must go south with him and learn the truth." The alliance thus became the catalyst for Ned's fateful journey to King's Landing.

The Alliance Tested

After Ned's arrest and the outbreak of war, Catelyn traveled to the Eyrie to seek her sister's help. She brought Tyrion Lannister as a prisoner, hoping Lysa would support the Stark cause and provide the knights of the Vale for the coming conflict. But Lysa had changed during her years in King's Landing. She was fearful, paranoid, and utterly devoted to her sickly son Robert Arryn. When Catelyn arrived, Lysa refused to commit any troops. "The Eyrie is impregnable," she insisted. "No enemy could ever reach us up here." Catelyn argued that hiding would not protect them, but Lysa would not be moved. The alliance that should have brought the power of the Vale to bear against the Lannisters instead left Catelyn isolated, with only her uncle Brynden Tully—the Blackfish—choosing to leave Lysa's service and ride south with her.

Consequences and Collapse

The failure of the Tully-Arryn alliance had cascading effects. Without the knights of the Vale, Robb Stark's army was smaller and more vulnerable. Catelyn was forced to negotiate with the untrustworthy Walder Frey at the Twins to secure a crossing of the Green Fork, a deal that bound Robb to marry a Frey daughter. Meanwhile, Lysa's refusal to act left the Vale neutral, a decision that would later prove disastrous when she herself became a target. The alliance that had once seemed so promising—linking two of the great houses of the realm through marriage and shared purpose—crumbled under the weight of Lysa's fear and her son's frailty. The bond between the Tullys and the Arryns, forged in the sept at Riverrun, became a source of bitter disappointment rather than strength.