Inmodern Welsh orthography, caer is usually written as a prefix, although it was formerly—particularly in Latin—written as a separate word. The Breton equivalent is kêr, which is present in many Breton placenames as the prefix Ker-.
The term is thought to have derived from the Brittonic *kagro- and to be cognate with cae ("field, enclosed piece of land").[4] Although stone castles were largely introduced to Wales by the invading Normans, "caer" was and remains used to describe the settlements around some of them as well. An example is the Roman fortatCaernarfon, formerly known in Welsh as Caer Seiont from its position on the Seiont; the later Edwardiancastle and its community were distinguished as Caer yn Arfon ("fort in Arfon", the latter being a district name (Cantref Arfon) from "ar Fôn", "(land) opposite Môn or Anglesey").[2] However, the modern names of the Roman fort and Edwardian castle themselves are now SegontiwmorCastell Caernarfon, while the communities carry on the name caer.
Note that the term is not believed to be related to the Irishcathair ("city"), which is instead derived from Proto-Celtic *katrixs, *catarax ("fortification").[5][6]
Gildas's account of the Saxon invasions of Britain claimed that there were 28 fortified Roman cities (Latin: civitas) on the island, without listing them.[8] The History of the Britons traditionally attributed to Nennius includes a list of the 28, all of which are called "caer".[7][12] Controversy exists over whether this list includes only Roman cities or a mixture of Roman cities and non-Roman settlements.[13] Some of the place names that have been proposed include:
The Cumbric language was spoken in Northern England until the Medieval era in which the element caer ("fort") was used in naming places.[33] It also appears in Cornish place-names as Ker-.[33]
Caermote, Cumberland (Caermollt, "Fort of the wether")[33]
Cumbric and Pictish were Brittonic languages spoken in Scotland until around the 12th century, and caer ("fort") was a place-naming element in both languages.[33][35]
^More precisely, these English placename elements derive from Latincastrum ("fortified post") and its plural form castra ("military camp"), making them the more precise equivalent of the Welsh castell.
^Latin names according to Mommsen's edition of Nennius,[9] translations and modern equivalents according to Ford,[10]Ussher,[11] or as otherwise noted.
^Henry of Huntington previously ascribed it to Lincoln, which was followed until the 19th century, when Bradley placed it at Lichfield,[22] thinking it to be the Roman Letocetum. Instead, excavations have shown that Letocetum was located at nearby Wall instead.[10]
^Both Ussher and Ford use the transcription Lundein; with regard to Mommsen, note the similarity with Lindum, the Roman name for present-day Lincoln, and the generic name *Lindon, "lake".
^Coit is Welsh for "woods" or "forest". Ford takes the name as a single construction "Caer-Pensa-Uel-Coyt" ("Fort Penselwood"), while Mommsen and Ussher treat vel as the Latin word for or: "Cair Pensa or Coyt".[9][11]
^Jones, Gwilym; Roberts, Tomos (1996). Enwau Lleoedd Môn : The Place-Names of Anglesey. Bangor, Wales: University of Wales Press. p. 122. ISBN0-904567-71-0.
