First mentioned in records from 1211-12 as the castle of 'Loxeuth', this earthwork likely dates from around 1187 when it became the main Westmeath seat of the powerful de Lacy family. The fortification consists of a conical mound rising to a flat oval summit measuring 19 metres north to south by 15.5 metres east to west, with a crescentic bailey to the north separated by a shallow ditch. The site's strategic position, surrounded on three sides by water and defended by marshy ground to the west, made it an ideal defensive stronghold throughout its long history.

The castle changed hands numerous times over the centuries, passing from the de Lacys to King John in 1210, back to Walter de Lacy in 1215, and eventually to William Blunt through marriage in 1332. By then, Irish forces had burnt the castle and no buildings remained on site, suggesting the motte may have been abandoned in favour of a new stone castle elsewhere. The site saw renewed military importance during the turbulent 17th century when it was refortified in the 1640s, with stones from a nearby church chancel repurposed for construction during Cromwell's time. Sir Henry Piers, writing in 1682, described how the motte was separated from the mainland by a deep graff with earthen ramparts and bulwarks, accessed via drawbridge over a water-filled ditch.

The Jacobites refortified the site in 1690, adding pentangular bastions and defensive banks, but it fell to Williamite forces under Ginkel after a short siege in 1691. Archaeological evidence of this military past continues to surface; metal detector users have discovered iron slag, cannon balls, musket shot and coins in the peaty soil near the lake shore. Today, visitors can still trace the outline of the 17th-century fortifications, including remnants of the causeway that once carried a drawbridge, fragments of masonry from various periods, and the impressive earthworks that have survived centuries of Irish weather. The site represents a remarkable palimpsest of medieval and early modern military engineering, from its origins as a Norman stronghold to its final role as a Jacobite artillery fort.