Oath and Oath Fullfillment

[Gurthang]

Back when the horse-lords first came down to help Gondor, Eorl pledged that the Rohirrim would come to Gondor's aid in other times of trouble. As a result, they were given the land which became Rohan. That oath is key in the story because Theoden decided to follow it and went in haste to Minas Tirith. Had he not fulfilled this oath, the story would have had a much different ending.