When Julius Caesar, later to be Roman Emperor, invaded Britain in BC 54-5, the 'Celtic' tribes lived in the British Isles. Their Celtic languages still survive as 'Gaelic' in Scotland & Ireland, 'Welsh', in Wales, and 'Manx' in the Isle of Man, as well as 'Breton' in France.
The Romans brought Latin to Britain, which was part of the Roman Empire for over 400 years. But early English did not develop mainly from Latin. So it is unlike French, Spanish and Italian, which did come directly from Latin. 'Early English' was the language of tribes who invaded from the East, from what is now Germany. They spoke different dialects of a 'Germanic' language, from which modern German developed. This explains why German and English are often similar, as many of their words developed from the same original language.
In 878 AD, the Vikings invaded Britain from Scandinavia, bringing with them the Norse language, though this was similar to the old English or Anglo-Saxon language already used.
The dramatic arrival of the Norman army from France, led by King William the Conqueror in 1066, and the defeat of the English King Harold at the Battle of Hastings, brought very big changes to English life. The Normans brought with them the Old French language, which became the language of the Royal Court, and the ruling and business class
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