the ring-fort of the Englishmen
< Lios na Seirseanach “the ring-fort of the mercenaries, hired soldiers”

The earliest example (1609 ‘Lisnesharchanah’) shows that this placename did not originally contain the word Sasanach but rather the common noun seirseanach “mercenary, hired soldier” (? < sergent na Fraincise). This same development seirseanach (> sea(r)sanach) > Sasanach (cf. Ó Searcaigh, Foghraidheacht Ghaedhilge an Tuaiscirt, l.101, §233) is found in the name of the townland Corr na Sasanach/Cornasassonagh (#39457), within 20km of this place in the parish of Magheross in Co. Monaghan.

Ó Dónaill and Ó Duinnín give the spelling seirseanach; Dwelly has searsanach, séirseanach; and A Dictionary of the Irish Language has seirsénach, -sen-, giving the explanation “‘an archer, a bowman’, O’Don. Suppl., … … but the usual meaning seems to be a mercenary, a hired soldier”. See also the extract below from Katherine Simms, ‘Gaelic Warfare in the Middle Ages’ in A Military History of Ireland:

Sometimes these bands of cavalry [on cattle-raids] were reinforced by armoured footsoldiers. Since the campaigns described in the ‘Triumphs of Turlough’ took place in Munster during the late thirteenth and early fourteenth centuries, there is no mention here of the Scottish galloglass who were already playing an important military role in north Connacht and Ulster by this date, but a very similar function was fulfilled by regiments of Anglo-Norman or Welsh auxiliaries serving with the Irish kings as political allies or simple mercenaries. Such a regiment was termed in Irish a rúta (from the French route) and an individual Welsh or English mercenary a seirseanach (perhaps from the French sergent). Like the galloglass these men are referred to as wearing armour and wielding battle-axes.

In 1313, according to the ‘Triumphs of Turlough’, King Muircheartach O’Brien was assisted by ‘William Burke’s route’. This could be an early reference to MacQuillin’s Route, a band of mercenaries about whom we know or can reconstruct rather more than usual. The ‘William Burke’ in question was certainly Sir William Liath de Burgh, cousin to Richard de Burgh the ‘Red Earl’ of Ulster. The rúta may well have been the troop of 200 seirseanaigh, also described as a retained band (cethern) of billeted soldiers or ‘bonaghts’ (buannaidhe) under the command of Johnock (Seonac) MacQuillin, who took service with Sir William de Burgh in 1310, having been bribed to assassinate their former employer, Aodh Breifneach O’Conor. Thereafter, the annals tell us, William de Burgh billeted these 200 men on the Irish of Roscommon, and there was a ‘bonaght’ quartered on every townland as long as he retained control of the area.

Cf. also the minor name Leaca na Seirsineach, Mallabracka townland, par. Fanlobbus (see O'Donoghue, Place Names of West Cork, 73), and the townland name Lios na Seirseán, par. Cullen, Co. Cork.

Creag na Sasanach/Craignasasonagh, par. Sainfield, Co. Down, is the earliest-attested Irish (administrative) placename in which the word Sasanach is originally found (see the historical information at www.placenamesni.org). See also the placenames Cnoc an tSasanaigh/Knockatassonig (Co. Cork), Cnoc an tSasanaigh/Mounthanover (Co. Wexford), and Ceathrú an tSasanaigh/Carrowntassona (Co. Waterford) in the south of the country.