Auldearn Castle, originally known as Eren Castle, dates from at least the twelfth century AD as a charter was signed there by William the Lion in 1180. The castle consisted of a motte, a type of fortification traditionally associated with the Normans, which suggests construction during the reign of David I (1124-53). He had actively encouraged Normans to settle in Scotland as a means of bringing his unruly country under control. They brought their castle building skills with them prompting a flurry of mottes across the country both constructed by the new arrivals and by native Scots who imitated their castle designs. Moray was an area of particular concern as a Celtic revolt had recently occurred there and, by the time William the Lion signed the charter, Auldearn Castle was a Royal possession.
The castle's motte had a diameter of 59 metres and stood over 8 metres tall. Today there are no visible traces of a bailey although it is possible one could have existed to the east of the mound under the modern housing. The castle was destroyed in the late twelfth century when its Constable surrendered it to Donald MacWilliam. It was at least partially rebuilt as in 1308 William, Earl of Ross submitted to Robert the Bruce there. Precisely when it went out of use is unknown but it is unlikely occupation continued into the fifteenth century and certainly by the time of the Wars of Three Kingdoms it was abandoned save for a seventeenth century dovecot on the summit.
During the Battle of Auldearn (1645) it is possible the site was used by the Royalist artillery. A report for the National Trust of Scotland suggests the raised embankment along the summit of the motte may have been a hastily raised as an artillery emplacement prior to the battle.