Eblana

Eblana () is the name of an ancient Irish settlement which appears in the "Geographia" of Claudius Ptolemaeus (Ptolemy), the Greek astronomer and cartographer, around the year 140 AD. It was traditionally believed by scholars to refer to the same site as the modern city of Dublin. For example, the 19th-century writer Louis Agassiz used "Eblana" as a Latin equivalent for Dublin. More recent scholarship however favours the north County Dublin seaside village of Loughshinny due to its proximity to Drumanagh, an important trading site with strong links to Roman Britain; it has even been described as a bridgehead of a possible Roman invasion. There is no definitive proof to tie Eblana with any location, however, so its exact identity is still a matter of speculation.
Eblana as Dublin.
If the reference to a settlement in Ireland called "Eblana" is in fact the earliest reference to Dublin, this would seem to give Dublin a just claim to nearly two thousand years of antiquity, as the settlement must have existed a considerable time before Ptolemy became aware of it.
Eoin MacNeill writes that Eblana "cannot be Dublin, for no trace has been found in Irish records or tradition of anything approaching in character to a city on the site occupied by Dublin until the Norsemen fortified themselves here in 841" and speculates that Elbana "is certainly farther north than Dublin, probably on the coast of Louth".
Early Irish antiquarians, such as Sir John Ware and Walter Harris believed that the name "Eblana" in Ptolemy's "Geographia" was in fact a corruption of "Deblana", itself a version of the Gaelic name "Dubh Linn" (Black Pool), from which the modern English language name "Dublin" derives. This seems not to be the only instance where Ptolemy truncated the initial letters of place names. For example, instead of "Pepiacum", and "Pepidii" (in Wales), Ptolemy writes "Epiacum" and "Epidii"; and for "Dulcinium" (now Ulcinj, in Montenegro), he has "Ulcinium". 
There are several problems with this theory:
Eblana as other sites.
At the time when Ptolemy wrote the "Geographia" there were two significant areas of activity in north County Dublin. One was at the mouth of the river Delvin where two substantial groups of chamber tombs would have been clearly visible from the sea for several thousand years. As noted above Ptolemy often dropped the initial letters of names and a shift from "Ebhlana" to "Delvin" could be seen as a phonic shift possibility. The second area of international activity was based around the promontory fort of Drumanagh south of present-day Loughshinny, which was probably a trading post but may have been used as a potential bridgehead by Agricola. Thus it is only fair to say that the identity of Ptolemy's "Eblana" is as yet unknown, and identification with the city of Dublin is at best problematic and highly speculative. 