The Tain is actually the abbreviated title of the Irish legend of Tain Bo Cuailnge, or The Cattle Raid Of Cooley. It is one of the earliest and most enduring examples of Irish literature and it is considered an epic despite the fact that it is written in prose form and not as a poetic verse. It tells the story of the great cattle raid, an invasion of Ulster by the armies of Queen Medb and King Ailill of Connacht and their allies. The objective of the invasion was to carry off the great Brown Bull of Cuailnge.
The tale's hero is a legendary Ulster teenager by the name of Cuchulainn, otherwise known as the Hound of Ulster. He single-handedly keeps the invaders at bay and resists the attack whilst the rest of his countrymen are sick and unable to join him in the battle.
Traditionally, the Tain has been set in the First Century, before Christianity had a foot-hold. This is an age during which many legends of "ordinary" folk heroes became legend. The Tain is the main text in a group of tales called "The Ulster Cycle". There are three surviving written versions in Twelfth Century manuscripts. The first is written mostly in Old Irish, used primarily the First Century. The second is written in Middle Irish, spoken throughout Ireland and Scotland in the Twelfth Century, a language contemporaneous to Middle English and the ancestor of modern Goidelic languages Irish, Scottish and Manx.The third version is written in early modern Irish.
To produce this translation, Thomas Kinsella has used two partial texts in two Medieval manuscripts, and in order to bring the tale to life includes related stories that act as an introduction to what actually happens in the Tain. Some were originally composed as stand-alone tales and others were written to stand alongside the Tain.