The mound, measuring 13 metres north to south and 11 metres east to west, rises between 0.4 and 3 metres high depending on where you measure from. It sits at the southern end of a ridge, in a field that locals still call the Moat field. The 1836 Ordnance Survey map confidently labelled this spot as the “Site of Siddan Castle”, showing it as the southwestern corner of an embanked enclosure, though there’s actually little evidence beyond these historical maps to confirm the castle stood precisely here.

The castle’s history stretches back to at least 1640, when John Fleming of Siddan owned both the castle and 500 acres of surrounding land. By the time of the Down Survey maps of 1656-8, which documented land ownership across Ireland following the Cromwellian conquest, two ruinous buildings were shown at Suddan on the barony map of Slane; one of these ruins was likely the castle, positioned roughly where the mound stands today. The Down Survey also included the neighbouring townland of Polecastle to the east within its depiction of Siddan.

Later maps tell a slightly different story about the area’s ruins. Taylor and Skinner’s 1783 map shows two ruins at Suddan, positioned south of the old road between Ardee and Kells, about 250 metres south of the current site. By 1837, the Ordnance Survey was depicting the location as both a ruined castle and a fragment of a ringfort bank, suggesting the site may have had an even older history predating the medieval castle. Whether the flat-topped mound visitors see today represents the actual foundations of Fleming’s castle, an earlier ringfort, or simply a convenient local landmark that became associated with the castle’s memory remains an open question.