"broad valley of the Clyde", Welsh: Ystrad Clud, Latin: Cumbria)[1] was a Brittonic kingdom in northern Britain during the Middle Ages.

In its early days it was called the kingdom of Alt Clud; the Brittonic name of its capital, and it controlled the region around Dumbarton Rock.

[4] The final period of Roman Britain saw an apparent increase in attacks by land and sea, the raiders including the Picts, Scotti and the mysterious Attacotti whose origins are not certain.

No historical source gives any firm information on the boundaries of the Kingdom of Strathclyde, but suggestions have been offered on the basis of place-names and topography.

Near the north end of Loch Lomond, which can be reached by boat from the Clyde, lies Clach nam Breatann, the Rock of the Britains, which is thought to have gained its name as a marker at the northern limit of Alt Clut.

Excepting the 6th-century jeremiad by Gildas and the poetry attributed to Taliesin and Aneirin—in particular y Gododdin, thought to have been composed in Scotland in the 6th century—Welsh sources generally date from a much later period.

The first is Coroticus or Ceretic Guletic (Welsh: Ceredig), known as the recipient of a letter from Saint Patrick, and stated by a 7th-century biographer to have been king of the Height of the Clyde, Dumbarton Rock, placing him in the second half of the 5th century.

Rhydderch was a contemporary of Áedán mac Gabráin of Dál Riata and Urien of Rheged, to whom he is linked by various traditions and tales, and also of Æthelfrith of Bernicia.

The Christianisation of southern Scotland, if Patrick's letter to Coroticus was indeed to a king in Strathclyde, had therefore made considerable progress when the first historical sources appear.

Broadly speaking, they have tended to produce theories which place their subject at the centre of the history of north Britain in the Early Historic period.

At the beginning of the 7th century, Áedán mac Gabráin may have been the most powerful king in northern Britain, and Dál Riata was at its height.

Áedán's dominance came to an end around 604, when his army, including Irish kings and Bernician exiles, was defeated by Æthelfrith at the Battle of Degsastan.

It is supposed, on rather weak evidence, that Æthelfrith, his successor Edwin and Bernician and Northumbrian kings after them expanded into southern Scotland.

Such evidence as there is, such as the conquest of Elmet, the wars in north Wales and with Mercia, would argue for a more southerly focus of Northumbrian activity in the first half of the 7th century.

[10] In 642, the Annals of Ulster report that the Britons of Alt Clut led by Eugein son of Beli defeated the men of Dál Riata and killed Domnall Brecc, grandson of Áedán, at Strathcarron, and this victory is also recorded in an addition to Y Gododdin.

In the last quarter of the 7th century, a number of battles in Ireland, largely in areas along the Irish Sea coast, are reported where Britons take part.

[11] The Annals of Ulster in the early 8th century report two battles between Alt Clut and Dál Riata, at "Lorg Ecclet" (unknown) in 711, and at "the rock called Minuirc" in 717.

The siege and capture are reported by Welsh and Irish sources, and the Annals of Ulster say that in 871, after overwintering on the Clyde: Amlaíb and Ímar returned to Áth Cliath (Dublin) from Alba with two hundred ships, bringing away with them in captivity to Ireland a great prey of Angles and Britons and Picts.King Arthgal ap Dyfnwal, called "king of the Britons of Strathclyde", was killed in Dublin in 872 at the instigation of Causantín mac Cináeda.

A number of place-names, in particular a cluster on the coast facing the Cumbraes, and monuments such as the hogback graves at Govan, are some of the remains of these newcomers.

However, historians are sceptical of the claim as Edward's power was confined to southern Britain, and they think it was probably a peace settlement which did not involve submission.

The names of Strathclyde's rulers in this period are uncertain, but Dyfnwal is thought to have been king in the early tenth century, and he was probably succeeded by his son Owain before 920.

According to the thirteenth-century chronicler Roger of Wendover, Edmund had two sons of Dyfnwal blinded, perhaps to deprive their father of throneworthy heirs.

[15] If the kings of Alba imagined, as John of Fordun did, that they were rulers of Strathclyde, the death of Cuilén mac Iduilb and his brother Eochaid at the hands of Rhydderch ap Dyfnwal in 971, said to be in revenge for the rape or abduction of his daughter, shows otherwise.

Some time after 1018 and before 1054, the kingdom of Strathclyde appears to have been conquered by the Scots, most probably during the reign of Máel Coluim mac Cináeda who died in 1034.