Little is known of the early life of Geoffrey of Monmouth. We believe that he was born sometime around 1100 in Monmouthshire (now Gwent). He entered the church, and served for over 20 years as a Master at the College of St. George in Oxford. This post certainly implies that Geoffrey was a learned man, according to the standards of his time.

It was during his time in Oxford - probably around 1136 - that Geoffrey produced his great work 'Historia Regum Britaniae' (The History of the Kings of Britain), which was a sort of national genealogy - however dubious it may have been.

Geoffrey claims that his Historia drew heavily upon an "ancient book" loaned to him by Walter, Archbishop of Oxford. It is also highly likely that he drew on a wide range of historical material - some of which is preserved in the Welsh Mabinogion, but also on oral tradition and the works of Bede, Nennius, and Gildas.

Geoffrey's work came at a time of turmoil in England; the country was torn apart by civil war as King Stephen and Queen Maude struggled for ascendancy. At the same time, Welsh national feelings ran high, fanned by Owain Gwynedd and his revolt in northern Wales.

Geoffrey's Historia is obviously coloured by his hopes for his homeland - he emphasizes the heroic past of the Britons, including the remarkable suggestion that they originated in ancient Troy.

Within this account of his Celtic ancestor's great deeds, Geoffrey provides the first complete version of the King Arthur legend then present in the folk tales of Wales and Brittany.

Geoffrey certainly did not invent the King Arthur legends, but he gathered together several strands of myth and history and retold the stories in a more "modern" medieval fashion.

Geoffrey of Monmouth was most probably also responsible for Vita Merlini, (The Life of Merlin), which appeared about 1150. These works together helped give a sense of national identity to the diverse Saxon, Norman, and British inhabitants of the British Isles, and provided much material for later writers to embellish.

Is Geoffrey's work history? Not in the way we think of history today, but it is likely that there was a firm basis of historical fact beneath the romantic tales of Arthur and Merlin.

But the Historia did more than popularize the Arthurian tales; it provided a sort of national genealogy - however dubious it may have been. Geoffrey was the first to tell the tale of King Leir, later immortalized by Shakespeare as King Lear.

Many of Geoffrey's "fanciful" tales have been proved by modern archaeological research to be founded in fact. For example, Geoffrey refers to contact between the British leader Pascent, and the Irish. This was long thought to have been a fictional invention, but recent discoveries of stones in Wales bearing Irish ogham inscriptions tend to support the tale.

In 1151 Geoffrey was appointed Bishop of St Asaph in Flintshire. It was there that he died in 1155.