The 10 strongest castles in Ireland

The largest Anglo-Norman castle in Ireland, roughly three acres inside a curtain wall studded with mural towers and gates, wrapped by a moat, its cruciform great keep of twenty corners rising on high ground above a ford of the River Boyne. Built by Hugh de Lacy from the 1170s, it was the caput of the Lordship of Meath.

That scale was never truly tested by siege. The earlier ringwork was burnt by Ruaidri Ua Conchobair in 1173, before the stone castle rose; the finished fortress has no record of withstanding an assault. In 1649 its garrison simply fled after Cromwell stormed nearby Drogheda, and Trim was occupied without a shot. Imposing by design, undefeated mainly because it was so rarely attacked.

Set on a rocky promontory once surrounded by sea on three sides, Carrickfergus is Ireland's best-preserved Norman castle, a great rectangular keep behind a high polygonal curtain, an east gatehouse with portcullis and murder holes, and crossbow loops later joined by splayed gunports for cannon. Water covered most of the perimeter, leaving one narrow landward approach to defend.

In eight centuries it was besieged by Scots, Irish, English and French. King John took it in 1210; Edward Bruce's Scots blockaded it for a full year from 1315, the starving garrison reputedly eating captured hostages before surrendering on terms in 1316 once a relief attempt failed. Schomberg's Williamites forced a surrender within a week in 1689 as the powder ran out, and a French squadron under Thurot seized it in 1760. Formidable, but never unbreached.

A stone fortress on King's Island in the Shannon, guarding the river crossing behind a curtain wall anchored by massive round drum towers and a twin-towered gatehouse, with a later bastion cut in for artillery. The river and the city walls covered its flanks.

It endured five sieges in the 1600s. In 1642 Garret Barry, having no guns, dug mines to undermine the walls; the garrison surrendered just before the foundations gave way, and excavations beneath the castle later uncovered the mine and countermine galleries of that siege. Ireton's Cromwellians took the city in 1651; in 1690 the defenders threw the Williamites back, earning Limerick its name as 'the unconquered city,' before the castle finally surrendered in 1691.

Athlone holds the great crossing of the Shannon, the gateway between Leinster and Connacht, a polygonal keep raised on a motte within a drum-towered curtain, built to command the bridge that was the whole point of the place.

In 1690 Colonel Grace refused Douglas's summons and the Williamites, lacking heavy guns, withdrew after a week. They came back in June 1691 under Ginkel with the heaviest bombardment yet seen in Ireland, some 32 guns and mortars firing close to a shot a minute, over 12,000 cannonballs and 600 bombs. The Jacobites broke the bridge and Sergeant Custume's volunteers died holding the gap; the town fell on 30 June only when grenadiers waded a ford and stormed it from the flank.

One of the largest and best-preserved castles in Ireland, Cahir sits on a rock island in the River Suir, ringed by water with a keep, curtain and towers that earned it a name for being impregnable. That reputation did not survive contact with artillery: in 1599 the Earl of Essex battered it into submission in just three days, one of the few Irish castles actually reduced by siege guns in the period. In 1650 it surrendered to Cromwellian forces under Inchiquin without a shot fired. Formidable to look at, but twice given up rather than held.

Dundrum crowns a rocky hill above Dundrum Bay in County Down, its defences climbing the outcrop, a massive round keep, a stone curtain hugging the rock, a rock-cut ditch and a twin-towered gatehouse modelled on Pembroke. Height and ditch made a direct assault hard, and John de Courcy's attempt to retake it failed in 1205. It could not stay in one hand for long, though: King John took it in 1210, the Earl of Kildare in 1517, Lord Deputy Grey in 1538, and it yielded to Mountjoy in 1601 before Parliamentarians slighted it in 1652.

Dunamase is a natural stronghold before it is a built one, a rock rising some 46 metres above the plains of Laois, its approaches climbing through a barbican and successive gates and curtain walls to the hall on the summit, so the position itself did much of the defending. Its documented record of pitched siege is thin, and its end came not in battle: in 1650 Cromwellian forces slighted the rock to stop it being used again, leaving the ruin that stands today. A commanding site with more natural than engineered strength.

Carlow guarded the River Barrow crossing on the edge of the Pale with a distinctive four-towered keep, a tall rectangular block clasped by three-quarter-round towers at each corner, but it had no towered curtain and no gatehouse, so the keep itself was effectively the whole defence. A frontier target, it was raided through the medieval wars and taken by Cromwellian forces in 1650. Its destruction, though, was not military: in 1814 a physician converting it into an asylum used explosives to open it up and brought most of the castle down, leaving only one wall and two towers standing.

The Maguire chiefs' stronghold stood on an island in the River Erne between the loughs, a keep and bartizaned curtain guarding the water route into Fermanagh, later gaining its distinctive Watergate. It was a prize in the Nine Years' War: Captain Dowdall besieged and took it in February 1594 after a short siege, the garrison massacred once they had surrendered. The next year Hugh Maguire's effort to recover it triggered the Battle of the Ford of the Biscuits, and the Irish did retake it in 1595, holding on until 1602. A small but genuinely fought-over frontier fortress.

Bunratty is the largest and most complete tower house in Ireland, a tall 15th-century keep with corner towers, machicolations and murder holes, placed to command the Shannon estuary approach to Limerick, but it is a fortified residence more than a purpose-built siege fortress. The successive castles on the site were taken again and again, earlier structures falling in 1284 and in 1318 after the Battle of Dysert O'Dea. The present tower house saw its main action in 1646, when Confederate forces under Lord Muskerry besieged its Parliamentarian garrison and Admiral Penn surrendered on terms. Strong for its type, but not in the class of the great curtain-walled fortresses above.