Although Dublin was the centre of the Viking kingdom in Ireland the Vikings did not give it a Nordic name. They referred to it by the Irish name Dubh Linn or 'black pool', which must originally have denoted the place where the River Poddle flowed into the Liffey and where the Vikings anchored their ships and built a stronghold on the nearby hillock. The Irish continued to refer to the settlement as Áth Cliath 'ford of the wattles', which originally denoted the strategically important ford upstream from the black pool, where the Liffey ceases to be tidal and at the meeting-point of the four principal roads of Ireland. The contribution of the Vikings to the employment of Dublin as the internationally known name of the Irish capital city is simply that it was this name rather than that of the ford that was taken over into the English language.
It was once thought that the Vikings who came to Ireland settled mostly in urbanised coastal strongholds, giving these Nordic names, for example Carlingford (*kerlingafjörth 'the fiord of the old hags', probably referring to the three mountain tops known today as The Three Nuns, which are used as a pilot point for entry into Carlingford Lough), Wicklow (*vík-ló 'grassy meadow by the creek'), and Waterford (*vethr-fjörth 'the creek with the male sheep or weather'). It is clear, however, that the Vikings must have exercised control over a fairly extensive hinterland to each of their strongholds. They could not have relied entirely on pillage and import but needed to have an assured local supply of food and other necessities. The hinterland of Dublin, for example, the region referred to by the Icelanders as Dyflinnar skíri or 'Dublinshire' and the northern part of which was known by the Irish as Fingal (Fine Gall) or 'the land of the foreigners', must have been very extensive, stretching north towards Skerries, south towards Wicklow and west as far as Leixlip. Leixlip is a Nordic name, *Lax-hleypa or 'salmon leap', reflecting the importance to the Viking community in Dublin of salmon-fishing in the Liffey. Corresponding to the 'shire' of Dublin Waterford had its Gaultier or 'land of the foreigners'.
Apart from the Viking strongholds, the surviving place-names of Nordic origin in Ireland are mostly the names of islands and headlands along the eastern and southern coastlines. Many of these were probably given to navigation points that were employed by Viking seamen who plied the routes across the Irish Sea as for example the above-mentioned Carlingford. Howth is the Nordic name of the peninsula that forms the north side of Dublin Bay. The name is Nordic *höfthi, related to the word for 'head', for the promontory is linked to the mainland by a narrow neck of land. The Vikings would frequently have sailed past its steep cliffs on their way to and from Dublin. Howth is still referred to in Irish by its old name Beann Éadair 'the peak of Édar'. Édar is supposed to have been the name of a legendary hero but it seems more likely that it was in fact the even older name of the locality, namely Edrou or Adrou, meaning 'the seat', a name which is ascribed in Ptolemy's 2nd-century geography to an uninhabited island off the east coast of Ireland and which probably referred to Howth.
Many of the islands around Ireland served multiple purposes in the Viking Age. Lambay Island (*lamba-ey 'lamb island') north of Howth was plundered by the Vikings in 795. The island was used for fattening lambs in the summer months but Lambay is not related to the Irish name Rechru (1308). This name is obscure but it probably means something like 'indented or rugged island'. Dalkey, the island at the south end of Dublin Bay, was used by the Vikings as a place of refuge after a defeat in 944 and at other times for holding prisoners. Its Nordic name (*dalk-ey 'thorn island') would seem to be a translation of the first part of the Irish name Deilginis Cualann 'the thorn island of Cuala', recorded as early as 733. The Nordic semi-translation points to a degree of linguistic contact between the Irish and the Vikings, as perhaps also does the name Ireland's Eye of the tiny island just north of Howth, which the Vikings had used as a place of refuge in 902. This name is probably an erroneous translation of the Irish name Inis Ereann 'the island of Eria (a feminine personal name that became confused with the Irish name for Ireland.
There are also a number of Nordic place-names around the coastlines of Wales. Most of these names would seem to be those of navigation points of strategic importance for Viking seamen. Great Orme or Ormes Head (Ormeshede in the 15th century), for example, is the name of a prominent headland near Llandudno in North Wales that was probably given this name (Nordic *orms-höfuth 'snake’s head') because its shape resembles the undulating body of a snake, strikingly so when seen from the air. Significantly, however, the promontory had an old Welsh name that was entirely unrelated to the Nordic one, namely Cyngreawdwr Fynydd 'the hill of the assembly', and it is known in Welsh today as Pen y Gogarth 'the hill of the terrace'. No linguistic communication between the Vikings and the Welsh was involved in this case. Another landmark with a Nordic name is Stack Rock, the name of a pillar of rock in the sea off Pembrokeshire. This is first recorded as the Stack(e) in 1594 and it is an example of a Nordic topographical word stakk 'pillar-shaped rock' functioning as a place-name.
The Vikings did not establish fortified urban centres in Wales but there is some evidence for Viking settlement there. The island now known by the Nordic name Anglesey still retains the Welsh name Ynys Môn. The Welsh name is a pre-Viking one, apparently identical with that of the Isle of Man, while the Nordic name *Önguls-ey would seem to mean 'island of (an unidentified) Öngul'. Anglesey was a target for numerous Viking raids, as well as trade, and Red Wharf Bay on the north-eastern coastline provided a sheltered haven for those sailing between Dublin and Chester. In the 9th and 10th centuries the settlement at Llanbedrgoch 'the red church of (St) Peter' gradually developed from a farm into a trading centre and excavations have produced many Viking-period finds there but no trace of a Nordic name for the settlement.
Milford Haven and Swansea, however, would seem to have developed as commercial centres and both towns were given Nordic names in addition to their older Welsh ones. The name Milford (Mellferth 1207) would seem to be a Nordic compound of mel 'sand-bank' and fjörth 'fiord', while the Welsh name Aberdaugleddau means 'estuary of the rivers called Cleddau'. Swansea is first recorded on coins minted in about 1140 as SWENSI and in a document from the second half of the 12th century as Sweynesse. This name is to be explained as the Nordic personal name Svein plus either sær 'sea' or ey 'island', while the Welsh name, first recorded in about 1191 as Abertawe means 'mouth of the river Tawe'. Another settlement with a surviving Nordic name is Fishguard in Pembrokeshire, originally *fiskigarth 'an enclosure for catching or keeping fish' and there are parallels to Fishguard in Normandy, the Isle of Man and Cumberland. Fishguard also has a Welsh name Abergwaun 'mouth of the river Gwaun'. One of the reasons for the survival of the Nordic settlement names Milford Swansea and Fishguard to the present day may simply be that the Scandinavian words involved resemble English words. The Nordic names are not related to the Welsh ones.
The survival of many Nordic place-names borne by small islands off and along the south coast of Wales, however, seems to reflect the existence of a Viking trade-route between Dublin and the Severn estuary, although several of these islands are known to have been the homes of monks or hermits. There were monastic communities, for example, on Ramsey (Ramesey 1293 'Rafn's or hramsa 'wild garlic' island') and Caldey (Caldea 1100-35 'cold island'), and probably hermitages on Grassholm (Grasholm 15th century 'grass island') and Gateholm (Gateholme 1480 'goat island'). Most of these islands had older Welsh names but there is no linguistic relationship between the Welsh names and the Nordic names they supplanted on the maps if not in Welsh speech. Ramsey was earlier Ynys Devanog 1722 'Tyfannog's island' and later Ynis Dewi 1825 'St David's islandi; Caldey was earlier known as Insula Pyrus 864 'Pir's or Pyr's island' while Grassholm is referred to as Gwales 'refuge'in 12th-century legendary sources.