Aldburg (OE. 'Old Fortress') is one of the oldest towns in Rohan, It is recorded it was built by Eorl in the region known as the Folde, east of Edoras. The Kings of Rohan removed to Edoras after Brego, son of Eorl completed the Golden Hall, but many centuries later there were still nobles living there, including Eomer, son of Eomund.
Even though Aldburg was in the King's Lands as part of the Folde it was the location of the muster of the East-mark as it was the most convenient location. At the time of the War of the Ring, it was the home of king Théoden's nephew Éomer, who was Third Marshal of the Riddermark.