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Because Robb needed to cross the Green Fork of the Trident, he pledged to Lord Frey (in his own castle!) to marry one of his daughters/granddaughters. Robb double-crossed Lord Frey, and the rest is history. Anyway...

Did Robb choose to cross at The Twins (Lord Frey's castle) because:

  1. There were no other possible ways for Robb's small expeditionary force to cross the Green Fork?
  2. While there are other good places to cross (even large armies), crossing at The Twins allowed Robb to attack the Lannister army from the best tactical position?

If there were no bridges at The Twins, how would the North and South be connected? Only small boats and minor bridges? Or, are there other big crossing points somewhere?

marked as duplicate by Skooba, Jason Baker, Aegon, Himarm, Adamant Jul 7 '16 at 16:52

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    Relevant: Why did Robb engage both Jaime and Tywin simultaneously . You will be able to see the maps for this action in that answer. Also, there was crossing at Ruby Ford. Tywin Lannister was moving to block it. Robb had no chance against Tywin so he successfully tricked both Tywin and Jaime and won a crucial victory at Riverrun after crossing the Twins. – Aegon Jun 22 '16 at 15:24
  • @Aegon You agree that there can't be any major troop movements over the Green Fork between The Twins and Ruby Ford? – Just Someone Jun 22 '16 at 17:32
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    not unless you have a fleet of boats to build you a bridge, no. Freys built their castle as bridge precisely because of this factor. Trident is a huge river which can't be forded easily. – Aegon Jun 22 '16 at 19:25
  • @khyle I am fairly certain it is cannon that the Twins are the only possibility to actually cross the Green Fork. You can go north until the river becomes small and shallow enough, which is quite far north, or you go south to Ruby Ford and thats that. However, I never understood these waters. The the Blue Fork is a sizeable river, the Green Fork a big river and even the Red Fork is a big enough river to host Riverrun. The Trident must be either a lake or a big and honking river, that it's hard to believe there can be such a thing as a ford. They say it's a river IIRC. – user1129682 Jun 23 '16 at 11:47

This is answered in the book A Game of Thrones (on which the first season of the TV series Game of Thrones is based):

"There's no crossing on the Green Fork above the ruby ford, where Robert won his crown. Not until the Twins, all the way up here, and Lord Frey controls that bridge. He's your father's bannerman, isn't that so?"

The Late Lord Frey, Catelyn thought. "He is," she admitted, "but my father has never trusted him. Nor should you."

"I won't," Robb promised.

In the next Catelyn-PoV chapter, they are approaching the Twins, their only option for crossing the Green Fork to reach Riverrun and engage Jaime Lannister in battle.

  • I'm sure that not having a crossing between The Twins and Ruby Ford is going to be a big issue. We will see! – Just Someone Jun 22 '16 at 17:30
  • That dialogue or something establishing the same thing was in the episode, too. They made sure to establish that Robb had to cross there, and thus had to make a deal with Lord Frey. – T.J. Crowder Jun 23 '16 at 7:14

Robb says bluntly in A Game of Thrones that the Crossing is the only way across the river:

“We must have the Twins, Mother,” Robb said heatedly. “There is no other way across the river. You know that.”

It's implied that they could ford the river depending on the conditions, but the Blackfish rules that out.

Robb turned back to Theon Greyjoy. “Has the Blackfish found any other way across the Green Fork?”

Theon shook his head. “The river’s running high and fast. Ser Brynden says it can’t be forded, not this far north.”

They could have gone further south or besieged the Twins, but Robb and Walder Frey both realize that time is of the essence.

“If you were strong enough to climb your own battlements, Lord Frey, you would see that my son has twenty thousand men outside your walls.”

“They’ll be twenty thousand fresh corpses when Lord Tywin gets here,” the old man shot back. “Don’t you try and frighten me, my lady. Your husband’s in some traitor’s cell under the Red Keep, your father’s sick, might be dying, and Jaime Lannister’s got your brother in chains."

tl;dr, usually you can avoid the Twins with extra time and effort, but Robb needed to cross the river and needed to do it immediately.

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