The Metrical Dindshenchas

Dindsenchas or Dindshenchas (modern spellings: Dinnseanchas or Dinnsheanchas or Dinnṡeanċas), meaning "lore of places" (the modern Irish word dinnseanchas means "topography"), is a class of onomastic text in early Irish literature, recounting the origins of place-names and traditions concerning events and characters associated with the places in question. Since many of the legends related concern the acts of mythic and legendary figures, the dindsenchas is an important source for the study of Irish mythology. Dinnseanchas can also refer to an Irish journal which discusses placename meanings.

The literary corpus of the dindsenchas comprises about 176 poems plus a number of prose commentaries and independent prose tales (the so-called "prose dindsenchas" is often distinguished from the "verse", "poetic" or "metrical dindsenchas"). As a compilation the dindsenchas has survived in two different . The first recension is found in the Book of Leinster, a manuscript of the 12th century, with partial survivals in a number of other manuscript sources. The text shows signs of having been compiled from a number of provincial sources and the earliest poems date from at least the 11th century. The second recension survives more or less intact in thirteen different manuscripts, mostly dating from the 14th and 15th centuries. This recension contains a number of poems composed after the Book of Leinster text. Dindsenchas stories are also incorporated into saga texts such as Táin Bó Cúailnge and Acallam na Senórach.

Although they are known today from these written sources, the dindsenchas are clearly a product of oral literature and are structured so as to be a mnemonic aid as well as a form of entertainment. They are far from an accurate history of how places came to be named. Many of the explanations given are made to fit the name and not the other way around, especially in the many cases where a place was much older than the Middle Irish spoken at the time of the poems' composition. In other cases, the dindsenchas poets may have invented names for places when the name of a place, if it had one, was not known to them. A detailed analysis points to a pre-Christian origin for most of the tales (http://www.jstor.org/pss/25508581). For example, many placenames appear which had fallen out of use by the 5th century A.D., when Irish written records began to appear in quantity.

...
Wikipedia