A motte and bailey, the most common form of early Norman fortification in Ireland, once stood in Killester, and by the 1920s a substantial portion of it was still visible. Today, nobody is entirely sure where it was.

A motte and bailey consists of a raised mound of earth, the motte, on which a wooden or stone tower would have stood, connected to an enclosed courtyard at ground level, the bailey, all typically surrounded by a ditch and bank. The Killester example is associated with a 12th-century house occupied by a man named William Brun of Killester, placing its origins in the decades following the Norman arrival in Ireland. The most detailed reference comes from Howlett, writing in 1979, who cited Father J. Kenny's History of Coolock Parish, published in 1934, to the effect that "a substantial portion of the surrounding moate and bailey survived up to the late 20's." That phrasing suggests Kenny himself, writing in the 1930s, was already describing something recently lost rather than something he could point to on a map. The tidying energies of suburban expansion did the rest.

There is, in practical terms, nothing to see here now, and that is precisely what makes the record worth knowing about. The exact location of the monument is listed as unknown, which means it lies somewhere beneath the roads, gardens, and houses of modern Killester, unexcavated and unconfirmed. For anyone walking the area today, the interest lies in the knowledge itself: that a Norman earthwork, already old when Dublin was a much smaller city, persisted into living memory before quietly disappearing. Local history collections and the archives of the Coolock Parish may hold the closest thing to further detail that survives.