The Norman Invasion marked the beginning of English Rule in Ireland but also brought great changes with the building of hundreds of earth and stone castles as well as new towns and great new cathedrals.
In 1169 Norman barons from Wales and England were encouraged to involve themselves in a dispute between King Diarmait Mac Murchada of Leinster and the High King of Ireland Toirdelbach Ua Conchobair. Initially welcomed by the Leinster faction and elements of the Church, the first Anglo-Norman expedition was followed in 1171 by a Royal Expedition under Henry II who landed at Dublin and established himself with papal support as Lord of Ireland. English rule over Ireland was never complete, while all of the major Irish dynasties submitted to the English Crown at one point or another; English royal authority was never consistently asserted over the entire island until the 17th century or 18th centuries. The existing Viking towns became thoroughly anglicised however and new towns were founded including what would become the medieval city state of Galway. Architecturally the period of English rule was characterised first by the construction of motte and bailey castles consisting of an earthen mound with a wooden palisade topped by a stone or wooden keep. Later these were followed by the construction of larger masonry castles such as the surviving examples at Knowth, Dowth, Trim Castle, Caisleáin na Circe and the great ringwork castle of Clonmacnoise.
The period was also characterised by major reforms and redevelopments of the larger monasteries and the large-scale appearance of stone churches. The eleventh, twelfth and thirteenth centuries marked a major period of church building, both as a result of English colonial expansion and prestige building by native lords. Many of the abandoned medieval churches, which still dot the Irish countryside, date to this period. The round tower at the monastery of Kilmacduagh in the Burren is still standing, the major period of construction at the island monastery of Skellig Michael was between the 10th and 12th centuries and the great density of surviving twelfth and thirteenth century churches on Aran reflects the islands’ relative wealth and significance as a pilgrimage destination.