, and, great as he was, the West Saxons within their
shrunken limits continued to be independent of him. He turned his
arms upon the Welsh, and drove them back from the Severn to the
embankment which is known from his name as Offa's Dyke. The West
Saxons, being freed from attack on the side of Mercia, overran Devon.
Then there was a contest for the West Saxon crown between Beorhtric
and Ecgberht. Beorhtric gained the upper hand, and entered into
alliance with Offa by taking his daughter to wife. Ecgberht fled to
the Continent.

28. =Mohammedanism and the Carolingian Empire.=--A great change had
passed over Europe since the days when a Frankish princess, by her
marriage with the Kentish Ethelberht, had smoothed the way for the
introduction of Christianity into England. In the first part of the
seventh century Mohammed had preached a new religion in Arabia. He
taught that there was one God, and that Mohammed was his prophet.
After his death his Arab followers spread as conquerors over the
neighbouring countries. Before the end of the century they had subdued
Persia, Syria, and Egypt, and were pushing westwards along the north
coast of Africa. In =711= they crossed the Straits of Gibraltar. All
Spain, with the exception of a hilly district in the north, soon fell
into their hands, and in =717= they crossed the Pyrenees. There can be
little doubt that, if they had subdued Gaul, Mohammedanism and not
Christianity would for a long time have been the prevailing religion
in Europe. From this Europe was saved by a great Frankish warrior,
Charles Martel (_the Hammer_), who in =732= drove the invaders back at
a great battle between Tours and Poitiers. Charles's son, Pippin,
dethroned the reigning family and became king of the Franks. Pippin's
son was Charles the Great, who before he died ruled over the whole of
Gaul and Germany, over the north and centre of Italy, and the
north-east of Spain. His rule was favoured both by the Frankish
warriors and by the clergy, who were glad to see so strong a bulwark
erected against the attacks of the Mohammedans. At that time the Roman
Empire, which had never ceased to exist at Constantinople, fell into
the hands of Irene, the murderess of her son. In =800= the Pope,
refusing to acknowledge that the Empire could have so unworthy a head,
placed the Imperial crown on the head of Charles as the successor of
the old Roman Emperors.

29. =Ecgberht's Rule. 802--839.=--Though Charles did not directl