Oath of Cirion and Eorl

After Steward Cirion had granted the land of Calenardhon to Eorl and his people, the two leaders met on the Hill of Anwar to swear perpetual allegiance to one another. This took the form of two oaths, collectively known as the Oath of Cirion and Eorl. Eorl swore his Oath first in his native language of the Éothéod, and Cirion replied in Quenya and in the Common Speech.

The day of the taking of the Oath was considered the first day of the new kingdom. Calenardhon would become known as Rohan, but the name 'Rohan' did not yet exist. So, after the making of the Oath, Eorl was granted the title King of the Mark of the Riders, and is accounted the first of the Kings of Rohan.