With the coming of the Angles, Saxons, and Jutes (and, apparently, Frisians) in 449, the island of England forever lost its Celtic character, and the era known as the "Anglo-Saxon" or "Old English" period began. The Celts were overrun, massacred, assimilated, or forced to retreat to the outermost edges of the islands, and the seafaring Vikings, speaking their own dialects of the West Germanic language, began their rule of the land. At first, there were seven kingdoms in all: Kent (settled by the Jutes); Essex, Sussex, and Wessex (settled by the Saxons); and East Anglia, Mercia, and Northumbria (settled by the Angles). These seven kingdoms are known as the Anglo-Saxon Heptarchy.
The Jutish settlements in Kent early on assumed dominance, owing to their superior wealth and culture. By the end of the sixth century the king of Kent, King Ethelbert, could call himself king of all the lands south of the Humber. During this period (in 597 A.D.), King Ethelbert was to receive St. Augustine, an emissary from pope Gregory I, who introduced Christianity to the islands and became in 601 the first Archbishop of Canterbury. Later the center of culture and political power shifted to the north, to Northumbria. There lay the great centers of learning at Lindisfarne, Wearmouth, and Jarrow (where Bede lived and wrote).
The power shifted to the south, to Mercia, and finally, King Egbert, king of Wessex, overthrew the Mercian rulers in 825 A.D. Egbert's grandson was King Alfred the Great, who ruled England as king from 871 to his death in 899.
In 787 occurred the first of many attacks by the "Vikings" or "Danes," as the Anglo-Saxons called them, marauding tribes of seafaring Scandinavians not far removed ethnically or linguistically from the Anglo-Saxon settlers themselves. For nearly one hundred years afterwards, these attacks continued and the Scandinavians slowly made their way down the island, conquering Northumbria and Mercia, pillaging and looting as they advanced. Finally, in 878 the Danish king ruling East Anglia and trying to expand his kingdom southward, Guthrum, was defeated by the English troops led by Alfred. Though the attacks would continue sporadically for another hundred years, in actuality England was restored to the English, and the Christian descendants of Alfred ruled Wessex and all of England.
During Alfred's time Wessex was the site of some of the most advanced cultures not only of England but of the entire continent of Europe. By the time of Alfred's death, the rulers of Wessex could without exaggeration call themselves "King of England."