Any trip through the Irish countryside, or looking carefully while in cities and towns, will reveal numerous square stone structures of 3-4 stories in various states of repair, from ruins in fields to currently occupied (the latter often integrated as part of later construction). If you consider these ‘castles’ then indeed Ireland is full of them. But these are properly termed ‘tower houses’ and very few of them had any fortifications beyond the building itself. They were most in vogue between 1450 and 1550 and there are few examples before 1400 or after 1600.

Instead of conflict - and they often include defensive features associated with military castles like arrow loops and trip stairs - they are archaeologically associated with regions and periods that are more stable and less contentious. It seems then that they were a fashionable way to take advantage of the fifteenth century’s prosperity and make a dramatic statement in the landscape. Gaelic, Old English/Anglo-Norman, and English leading families all built surprisingly similar looking ones, probably because they were based on Continental models rather than their neighbours.

Sources: Caoimhín Ó Danachair, ‘Irish Tower Houses and Their Regional Distribution’ Béaloideas 45 pp 158-163

Rory Sherlock, ‘The evolution of the Irish tower-house as a domestic space’ Proc RIA 111 pp 115-140

There are also several recent articles on them in Terry Barry and Vicky McAlister (eds) Space and Settlement in Medieval Ireland and Linda Doran and James Littleton (eds) Lordship in Medieval Ireland: Image and Reality.