'Hear now all peoples who bow not to the Shadow in the east,
by the gift of the Lord of the Mundburg
we will come to dwell in the land that he names
and therefore I vow
in my own name and on behalf of the Éothéod of the North
that between us and the Great People of the West there shall be friendship forever:
their enemies shall be our enemies,
their need shall be our need,
and whatsoever evil, or threat, or assault may come upon them
we will aid them to the utmost end of our strength.
This vow shall descend to my heirs,
all such as may come after me in our new land,
and let them keep it in faith unbroken,
lest the Shadow fall on them
and they become accursed.'
So said Eorl the Young at the tomb of Elendil and forever
bonded Rohan to Gondor in oaths with Manwë and Varda as witnesses.
By Cirion the Steward of Gondor, Eorl and his people were given the
area where Rohan took shape long after Gondor had abandoned much of its
lands further afield. Eorl became the first king of the Rohirrim and
the "Mark" which if I remember reading somewhere means "gift". He was
young and had gold hair and was to come to the aid of Gondor many
times, including at the Battle of the Field of Celebrant.
He fell at the Battle in the Wold and over him the first mound was raised.
He was succeeded by Brego .
References: Unfinished Tales, Lord of the Rings,
Tolkien Quiz Book