[Overtaxed]

Boromir came through the Gap of Rohan on his way to Rivendell, it was open then... And under Gandalf's leadership they were all hoping to go that way when they left.

That's why I wanted to look at ecurbh's timeline. Eomer tells Aragorn that Saruman closed the Gap but I don't know when in relation to the Council of Elrond. Gap-closing, horse-raiding, and border-skirmishes aren't exactly characteristic of neighbors who get along.

[HairOfTheDog]

Eomer and Aragorn did not meet until after the Council, on the plain when they were following Merry and Pippin.

[HairOfTheDog]

The Treason of Isenguard was not known until Gandalf escaped and was brought to Rivendell... Gandalf was the first to know that.