Built by the O’Donnell clan, the castle witnessed some of the most dramatic moments in Irish history. In 1522, it was burned during an O’Neill raid, whilst in 1592 it served as a stopping point for Red Hugh O’Donnell during his famous escape from Dublin Castle. The fortress truly proved its worth during the Nine Years’ War when Sir Conyers Clifford besieged it in 1597, positioning his troops and artillery at nearby Mullanshee Fort on the high ground.

The 1597 siege provides one of the most vivid accounts of castle warfare in Irish history. For three days, Clifford’s forces bombarded the walls with heavy artillery that could be heard for miles around, whilst armoured soldiers attempted to breach the defences using siege engines and protective shields. The castle’s defenders responded with withering fire from guns and muskets, hurling rocks, massive stones, timber beams and blocks from the battlements onto the attackers below. The assault proved futile; Clifford was forced to abandon the siege and lost many soldiers during his retreat south. Though the castle eventually fell to Henry Docwra in 1602, its defensive capabilities had been thoroughly demonstrated.

After the Nine Years’ War ended in 1603, the Dublin government retained the castle and its surrounding thousand acres, entrusting Sir Henry Folliott with establishing a plantation town. Folliott appears to have either rebuilt or substantially added to the existing structure, constructing “a fair and strong castle” of lime and stone, and the borough was officially incorporated in 1613. By the 19th century, only fragments remained; Hugh Allingham noted in 1879 that just a portion of one wall survived, about 10 feet high and 5 feet thick, incorporated into a grain store and butter shed near the market yard. Today, even these remnants have vanished, with only Castle Street preserving the memory of where this once formidable fortress controlled the crossing of the Erne.