The English marcher lineages, or, perhaps more accurately, those families or kindreds not of Gaelic descent who settled in the area now comprising south County Dublin following the arrival of the English, played an instrumental part in shaping the boundaries of what would by 1500 be known as the English Pale. There was a large number of these families living in this area from the 1170s, but for reasons of space we must limit the focus here to a specific few: of similar strength and drawn from a mixture of Scandinavian, Welsh and English ethnic backgrounds and inhabiting this compact district, the Harolds, Lawlesses, Howels, Archbolds and Walshes (or Walshmen) offer a broad perspective. The raison d’être of these five lineages occupying a border between two very different societies changed through the centuries, just as political and military conditions changed. The original motivation to colonise the district apparently reflected opportunism coupled with the Dublin administration’s desire to have English subjects moulding the adjacent countryside into a secure, profitable English entity. Yet Gaelic hostility — often manifesting itself in raids emanating from the nearby Leinster mountains — arrested the English colony’s southward expansion, and the role of the lineages assumed an increasingly military character.

When news arrived in summer 1580 that James Eustace, third viscount Baltinglass, had entered into rebellion with Gaelic elements in Leinster, Tudor officials in Ireland could barely contain their mystification. How, they wondered, had this important Tudor noble, whose family had for centuries served as a bulwark against the menace of marauding Gaelic clans, become ‘so forgetful of himself’? In seeking to explain the rebellion historians too have sought to understand Eustace's motivation, and in so doing have come to emphasize his integral position in conceiving and leading the revolt. Yet this approach has obscured the rebellion's Gaelic dimension. The rebellion would not have been possible without the support of the O'Byrnes and O'Tooles who sought to uproot the English county administration then being erected in place of their quasi-independent lordships. Fiach MacHugh O'Byrne emerged from this interest to become the rebellion's true strength and in August 1580 dealt a shattering defeat to the English army in Ireland.