Thank you for your corrections. Here are some more sentences on history I'm not sure of (especially the parts included in brackets).
1)The Celts were expert farmers (?), hunters and deep-sea fishermen.The Romans introduced (I need a synonym: brought?) their civilization and the Latin language (in England?).
2) They built towns connected by roads, which were later destroyed by some Germanic tribes, who invaded Britain in the 5th century.
3)In the 5th century the Romans had to retreat their soldiers from England to fight against (synonym) a Barbarian invasion (or Barbarian raiders/a Barbarian attack).
4)England was then invaded by some Germanic tribes, namely the Angles, the Saxons and the Jutes, who were organized in tribes.
5)The Anglo-Saxon invaders took away the Christianity which retreated into the western parts of the country. (Christianity retreated/or was retreated ?).
1)The Celts were expert farmers, hunters, and deep-sea fishermen. The Romans brought their civilization and the Latin language to England.
2) They built towns connected by roads, which<~~does "which" refer to roads or towns? were later destroyed by some Germanic tribes who invaded Britain in the 5th century.
3)In the 5th century, the Roman soldiers had to retreat from England to repel a Barbarian attack.
4)England was then invaded by some Germanic tribes, namely the Angles, the Saxons and the Jutes, who were organized in tribes.
5)The Anglo-Saxon invaders took away the Christianity which retreated into the western parts of the country. (Christianity retreated/or was retreated ?). <~~This whole last sentence is strange. Romans did not become Christian until around 400 AD, and Christianity didn't reach England until close to 600 AD. This sentence seems out of place, considering the contents of the other 4 sentences. Also "took away" and "retreated" seem odd verbs to use for these sentences. Let us know what you are thinking of, and we should be able to help you better.