Through the leadership of the kings of Gwynedd, the Welsh managed to defeat the Vikings. The churches in Wales are testimony today of the Danish threat, for they lie hollows, hidden from the sea. The Viking threat forced the Welsh to unite in order to defeat the marauding foe. The first important leader was Rhodri Mawr (Rhodri the Great), who in 855 became king of Powys. Through strategic marriages and alliances, Rhodri managed to control a great deal of Wales and to defeat the Viking, Gorm. Unfortunately, this unification was short-lived and following his death while fighting English incursion, Wales once again fell into internal strife. Rhodri's grandson, Hywel Dda (Howell the Good) managed to unite his territories in Deheubarth with those of Gwynedd and Powys. Hywel is remembered for his codification of the Welsh law. Based upon tradition, the Welsh law specified that a father's land be divided among all of his sons, rather than only the eldest. Unlike English law, Welsh law gave significan status to women by granting them certain property rights and rights of compensation for marital abuse as well as property rights in divorce. In welsh law, the rights of an illegitimate son to claim his patrimony is also protected

Rhodri ap Merfyn was styled Rhodri Mawr (the Great), son of Merfyn Frych (the Freckled). The Great signifies his acheivements and is only borne by two others of the period, Charles the Great (Charlemagne) and Alfred the Great. Forever after Rhodri's death, to be of the line of Rhodri was a qualification for Welsh rulers. Rhodri ruled over more than half of Wales and was known as a supreme warrior. Rhodri Mawr was the first to claim the title of King of the Welsh. Rhodri became king of Gwynedd in 844, following the death of his father. In 856, he defeated the Viking Horn at Angelsey in a battle which won him international reknown.

Through his mother, he inherited the kingdom of Powys in 855 with the death of his uncle, and with it, the ancient struggle with the kingdom of Mercia. He became king of Seisyllwg, including Ceredigion and Ystrad Tywi following the death of his brother-in-law in 872. This inheritance, along with his rule of Gwynedd made him ruler of all of northern and western Wales.

Rhodri showed the Welsh that through unification, they need not be subservient to the English. Rhodri was the greatest of all kings of Wales due to his creation of a national consciousness.

Rhodri and his son, Gwriad were killed in battle against the English in 878.

"According to the genealogies in Jesus College MS 20, Rhodri's mother was Nest of Powys, sister of Cyngen, king of Powys.

Cyngen is the Concenn who erected Eliseg's Pillar, in memory of his great-grandfather, Eliseg (Elisedd). Elisedd would probably have been a contemporary of the powerful Mercian king, Offa (757-796). The pillar commemorates Elisedd's reclamation of Powysian territory from the English, and the 'Annales Cambriae' record several campaigns against the Welsh by Offa. At some point, Offa seems to have decided that there should be no doubt where the border between the English and the Welsh lay, and the massive earthwork, known as Offa's Dyke was constructed. Whether Offa's Dyke was more symbolic than truly defensive is the subject of debate. Even if it prevented Welsh incursions into England, it certainly it didn't prevent English incursions into Wales. 'Annales Cambriae' (822): "The fortress of Degannwy (Gwynedd) is destroyed by the Saxons and they took the kingdom of Powys into their own control."

Cyngen died in 855 ('AC' 854), possibly having been forced into exile by Rhodri. Powys was subsequently annexed by Gwynedd. How this takeover was achieved is not recorded, but Powys was ruled as a subsidiary of Gwynedd until the late 11th century. In its entry for 853, the 'Annales Cambriae' had noted:

"Mona laid waste by black gentiles."

The phrase "black gentiles" (and in Irish annals "Dark Foreigners") means Danish, rather than Norwegian ("Fair Foreigners"), Vikings. The first recorded Viking attack on Wales actually appears in the 'Annales' against the year 850. They were responsible for the killing of one Cyngen, whose provenance is unknown.

In 856, however, as recorded by the Annals of Ulster, Rhodri won a famous victory against them:

"Horm (Gorm), chief of the dark foreigners, was killed by Rhodri son of Merfyn, king of Wales."

The 'Annals of Ulster' also provide a reminder that the Vikings weren't the only external threat that Rhodri had to contend with (865):

"The Britons were driven from their land by the Saxons (presumably Mercians) and were placed in bondage in Móin Chonáin (Anglesey)."

Nevertheless, Rhodri's empire building activities continued. Jesus College MS 20 shows him married to Angharad, sister of Gwgon of Ceredigion. Gwgon drowned (the circumstances are unrecorded), in 872 ('AC' 871), and control of Ceredigion was subsequently acquired by Gwynedd.

Ceredigion is still the term used in 9th century annals, but later tradition has it that (in the late 7th century) Seisyll, the king of Ceredigion, added the territory of Ystrad Tywi (literally 'Vale of Towy' - to the south of Ceredigion), and that the enlarged kingdom was thenceforth called Seisyllwg in his honour.

In 877, however, the 'Annals of Ulster' note that:

"Rhodri son of Merfyn, king of the Britons, came in flight from the dark foreigners to Ireland."

And a year later (878):

"Rhodri son of Merfyn, king of the Britons, was killed by the Saxons."

The 'Annales Cambriae', in its record of the event (which is assigned to 877), adds the additional information that Rhodri's son, Gwriad, was also killed.

Also in 878, Asser, reports that: ". . . the brother of Hingwar (Ivar 'the Boneless') and Halfdene (Halfdan), with twenty-three ships, after much slaughter of the Christians, came from the country of Demetia , where he had wintered, and sailed to Devon, where, with twelve hundred others, he met with a miserable death, being slain while committing his misdeeds, by the king's servants, before the castle of Cynuit (Countisbury), into which many of the king's servants, with their followers, had fled for safety."

Rhodri is remembered as Rhodri Mawr ('the Great'), the only Welsh king to be so honoured. The 'Annales Cambriae' record that, in 881 ('AC' 880), there occurred:

"The battle of Conwy. Vengeance for Rhodri at God's hand."

Presumably, it was, the Mercian king, Ceolwulf II who was responsible for the death of Rhodri - and also his forces who were defeated at Conwy.

After Rhodri's death, his son Anarawd, with his brothers, ravaged south and mid Wales. Asser reports that:

". . . king Hemeid (Hyfaidd), with all the inhabitants of the region of Demetia (Dyfed), compelled by the violence of the six sons of Rotri (Rhodri), had submitted to the dominion of the King (Alfred 'the Great' of Wessex). . . Helised (Elisedd), also, son of Tendyr (Tewdr), king of Brecon (Brycheiniog), compelled by the force of the same sons of Rotri, of his own accord sought the government of the aforesaid king . . . .

Anarawd, it seems, had entered into an alliance with the Northumbrian Danes.

. . . . and Anarawd, son of Rotri, with his brother, at length abandoning the friendship of the Northumbrians, from which he received no good but harm, came into king Alfred's presence and eagerly sought his friendship. The king received him honourably, received him as his son by confirmation from the bishop's hand, and presented him with many gifts. Thus he became subject to the king with all his people, on the same condition, that he should be obedient to the king's will in all respects . . ."." The Birth of Nations: Wales