55 BC

Cesar goes beyond “the end of the world” (Gaul) into Britannia and defeats the Celtic tribes occupying the south-eastern part (where London is today).

55

AD

The Romans, under the emperor Claudius, finish conquering most of the area that is today England: from the southern coast up to the Humber River in Yorkshire.
Actually, the Romans made occasional, unsuccessful attempts to conquer the north, above the Humber, for 70 more years. Finally, in 122 AD, they changed strategy and created a massive wall to keep the Scots (Pictish) and other northern Gallic tribes out: Hadrian's wall, still in existence.

408-410
AD

The Visigoths surround Rome (a “siege”) in 408 and 409 but do not enter. In 410 AD the Emperor Honorius tells the people in Britannia that Rome will no longer defend the Isle and calls the last Roman legionnaires stationed in Britain back to Rome. In vain, however.  In 410 the Visigoths manage to enter and sack Rome.  Honorius escapes to Ravenna and never returns. The Roman empire is over.

In Britain, the Celtic people ask Saxon pirates to establish fortresses along the coast to defend them from the Angles and the Jutes. The Saxons accept, but then attempt to conquer England for themselves. They are temporarily defeated by the Celts under Arthur (the legendary “king” with his “knights” of the round table).

550

There is a massive invasion of southern Britain by the Saxons (from what is Northern Germany today) and Frisians (from what is Northern Holland). There are also invasions of northern Britain by Angles and Jutes (from what is Denmark today).

The Celts escape to the North (today, Scotland), the West (today, Wales, Cornwall) and across the seas to France (Brittany – the land of Asterix) and of course to Ireland, where Celtic culture had been flourishing for centuries.  Scholars still dispute how many Celts remained in England: chromosome evidence indicates few if any.

The conquering Germanic tribes establish commercial and then political relations among each other and work out a common dialect -- what has become the English (Angle-ish) of England (Angle-land).