It is not known exactly when speakers of the Gallo-Brittonic form of Celtic first established themselves in Britain, but it must have been during the Iron Age, no earlier than ca. 600 BCE and no later than ca. 200 BCE. Both Britain and Ireland had, since the Late Neolithic, been a part of a flourishing "Atlantic" culture, where a variety of Celtic and pre-Celtic languages had no doubt been spoken. By the time Greek and Roman sources provide us with information on British personal and place names, the language they reflect seems little different from the Gaulish spoken by the Celts of the Continent, which is why it is generally referred to nowadays as "Gallo-Brittonic". Since the same Classical sources indicate that it was from the northern Celtic peoples known collectively as the Belgae that the latest and most influential settlers of Britain had come, it appears that the Belgic dialect came to predominate on the island and served as the basis for the later development of the Brythonic, or British Celtic, languages.

The Roman conquest of most of Britain in the first century CE established Latin as the language of administration and of all official business in urbanized areas, but British remained the spoken language of the countryside and of the independent tribal areas in the far north. When Roman rule collapsed in the mid-5th century and English settlers from across the North Sea took over much of the island, it was the most heavily Romanized areas in the east and the midlands that succumbed first, and native British chieftains from areas outside direct Roman control were able to consolidate their power in the north and the west. The language they used was British, not Latin; even so, their speech had adopted a large amount of Latin vocabulary from the centuries of Roman occupation, and this has remained as part of the heritage of the Brythonic languages.

By the 6th century British shows signs of developing in the direction of Welsh as we know it, but our main records of Old Welsh (Hen Gymraeg) come from the period between the 9th and the 11th centuries. The oldest ones are glosses on Latin religious manuscripts, but there was also a flourishing poetic tradition, much of it relating to parts of Britain far outside the present-day borders of Wales. The _Gododdin_, attributed to the bard Aneirin, describes a doomed raid by British Celtic tribesmen from the region of modern Edinburgh on the territories of their English enemies in Northumbria. Taliesin, the poet about whom a rich mythological tradition would later develop, praised and mourned his patron Urien the ruler of Rheged, a kingdom straddling what is now the border between Scotland and England. A strikingly beautiful cycle of poems is traditionally attributed (although the form of the language in fact belongs to a later period) to the 7th-century princess Heledd, mourning the death of her brother Cynddylan the ruler of Pengwern, in what would later become Shropshire, after it was overrun by the English. In Welsh literary history these poets are usually referred to as the _Cynfeirdd_ or "Proto-Bards".

From the end of the 11th century to the end of the 14th century the form of the language is called Middle Welsh (Cymraeg Canol). This is an extremely rich and creative period for Welsh literature. Native rulers (and, a little later, Norman overlords) received praise from formally trained, professional poets. They are known in Cymraeg as the _Gogynfeirdd_. Their work is very difficult to interpret, as it is less concerned with conveying a linear meaning than with creating impressions through sound-painting. Other, more accessible poems have been preserved from this period as well; and this was also the golden age of the _cyfarwyddiaid_, or professional storytellers, who (together with their counterparts in Cornwall and Brittany) played a major role in developing the stories that would become famous internationally as the Matter of Britain (or the Arthurian mythos), recycling ancient mythological themes as mediaeval entertainment. Eleven of these tales, preserved in the manuscript collections called the White Book of Rhydderch and the Red Book of Hergest, were published together in the 19th century by Lady Charlotte Guest under the title _The Mabinogion_, and are still counted among the classics of world literature. They are only the tip of the iceberg, however, a small part of a rich narrative tradition that is now mostly lost. The _Trioedd Ynys Prydein_ (Triads of the Isle of Britain), a work from the same period that was intended to serve as a mnemonic aid for _cyfarwyddiaid_ by grouping stories in triads according to salient narrative features, contains references to many stories that are otherwise unknown to us.

After the violent end of native rule in 1285, a slow cultural shift occurred throughout Wales. Cymraeg remained the everyday language of the country, and native poets continued to praise the nobility according to traditional custom, but the mysterious intricacies of the art of the _Gogynfeirdd_ became less and less appropriate for an upper class with increasingly foreign connections. In the course of the 14th and 15th centuries poets adapted their styles to the new cultural climate, importing forms and subject-matter from other European traditions while retaining and expanding the complex native approach to alliteration, or _cynghanedd_. These poets are known collectively as _Beirdd yr Uchelwyr_ (Poets of the Nobility). Dafydd ap Gwilym (ca. 1320-ca. 1380), perhaps the greatest Welsh poet and the greatest European poet of the 14th century, was something of a "hinge" figure, whose writings show the transition from Middle Welsh to Modern Welsh (Cymraeg Cyfoes).

The rise of the Welsh-descended Tudor dynasty to the English throne at the end of the 15th century didn't lead to a higher status for Welsh language and culture. On the contrary, the Tudors identified strongly with English as the sole language of a centralized state, and in 1532 merged Wales with England administratively, stripping the Welsh language of all official status. However, in their zeal for promoting the Protestant Reformation (which the Welsh at first strongly resisted), the Tudor government sponsored the translation of the Bible into Welsh: published in 1588, the Morgan Bible had an impact on the Welsh language comparable to that of the King James Bible on English. It helped create a pattern for writing in modern Welsh -- which also received some impetus from the work of Elizabethan Welsh "humanists" like William Salesbury. The masterworks composed in Cymraeg over the next century and a half include Morgan Llwyd's _Llyfr y Tri Aderyn_ (The Book of the Three Birds) and Ellis Wynne's _Gweledigaetheu y Bardd Cwsc_ (The Visions of the Sleeping Bard).

Towards the middle of the 18th century Bible-based literacy in Welsh helped in the spread of the Methodist revival movement through the medium of Cymraeg. Poets like Ann Griffith and William Williams Pantycelyn composed hymns that have remained a beloved part of the Welsh heritage to this day. The revival also established a Welsh-speaking "chapel culture" that dominated rural Wales until the second half of the 20th century.

By the end of the 1700's there were enough prosperous Welsh-speaking tradesmen both inside and outside Wales to bring about the emergence of a Welsh-speaking middle class. As a rule, these people were interested in their native heritage and sponsored the publication of early literary texts and documents in Cymraeg, especially under the auspices of fraternities like the Cymmrodorion and the Gwyneddigion. It was at this time that an erudite stonecutter from Glamorgan, Edward Williams (who took the bardic name Iolo Morganwg -- "Eddie from Glamorgan" --, by which he is far better known), got involved in the antiquarian research conducted by those societies. Iolo was a brilliant poet, but his over-fertile imagination led him to forge a huge number of texts chronicling a fictional "Druidic" history of Wales - accepted without reservation by his colleagues, who were dazzled by his brilliance and learning. Iolo's forgeries and fictions continued to have a major influence on Welsh culture throughout the 19th century. His creation of a _Gorsedd y Beirdd_ (a sort of "Druidical College", intended as an arbiter of Welsh moral and artistic life) and its subsequent placement at the heart of the National Eisteddfod (an _eisteddfod_ or "session" was originally a gathering of traditional poets who wanted to share their works and compete for prizes) added     a great deal of glamour and prestige to an event that remains one of the principal Welsh-language institutions to this day. In general, the sense that Cymraeg was a rich, ancient language with a romantic heritage worthy of international respect kept it on the lips of common people even when the Industrial Revolution uprooted many of them from their traditional rural communities and drove them into the coal mines. There was a flourishing Welsh-language press, and many local literary competitions and amateur theatrical groups      kept creative activity in the language alive even in urban areas. The sweet song-lyrics of John Ceiriog Hughes were known to everybody; and the modern Welsh novel had its beginnings with the works of Daniel Owen.

Around the turn of the 20th century a circle that grew up around the Oxford Welsh professor John Morris-Jones purged Welsh scholarship of its Iolo-ist fantasies and established it on a modern foundation. The period also saw the emergence of a large number of poets with powerful and original talents: Thomas Gwynne Jones, W.J. Gruffydd, Robert W. Parry, and T.H. Par ry-Williams, to name a few. Saunders Lewis, a Liverpool Welshman and a founding member of Plaid Cymru (the Party of Wales), shook up the establishment with his controversial outsider's views on Welsh culture and, as a playwright, was one of the primary forces in developing a modern Welsh-language theatre. Kate Roberts became justly famous for her brilliant short stories on modern Welsh life.

In spite of all this cultural creativity, however, the increased predominance of English in all areas of public life and -- especially after World War II -- the penetration of almost exclusively English-language mass media into every Welsh-speaking community led to a marked erosion in the use of Cymraeg over the 20th century. In 1962 Saunders Lewis made a famous radio speech entitled "Tynged yr Iaith" (the Fate of the Language) in which he warned the Welsh of the imminent extinction of their language unless they took decisive steps to preserve it. This inspired the creation of Cymdeithas yr Iaith Gymraeg (the Welsh Language Society) which, through both political lobbying and well-publicized acts of civil disobedience,     put the government on the defensive and gradually helped improve the public status of the language. One of the culminations of this series of campaigns was the creation of S4C, the Welsh-language BBC television channel, in 1982 after Gwynfor Evans -- then-president of Plaid Cymru -- threatened a hunger strike unless government pledges to launch the channel were honored. At first derided for its costliness, S4C survived its formative years and eventually opened up vast new employment opportunities for Welsh-speakers in the media. The 1980's also saw the rise of an indigenous Welsh-language youth/rock culture. The Welsh publishing scene remains very active, producing works in every literary field, from academic writing to romance novels. Stepped-up efforts at providing Welsh-language education have also paid off: the 2001 Census showed, for the first time in over a century, an increase in the absolute number of Welsh-speakers.

Nevertheless, all is not well. Welsh-speaking communities are still being flooded with English-speaking immigrants who have no interest in local culture and no intention of acquiring the local language, and who eventually eliminate the role of Cymraeg in local institutions. The continued erosion of the Bro Gymraeg -- the areas where Welsh is the natural language of everyday speech -- is a matter of grave concern, with serious implications for the future of the language.

There are marked differences between formal and colloquial styles of Cymraeg. While there is a "classical" literary style that most educated Welsh-speakers acquire and which is essentially the same throughout Wales, there are two major dialects of colloquial usage: North Welsh and South Welsh, which differ considerably in pronunciation, grammatical features, rules for contractions, and vocabulary. Although the largest groups of natural Welsh-speakers are in the North Welsh area, many learning materials stress South Welsh usage, since it is in South Wales that efforts to get people to re-learn Welsh have been most intense. Both dialects are equally prominent in the media.