Old English 450-1100 AD:
The invading Germanic tribes the Angles, the Saxons and the Jutes spoke similar languages, which in Britain developed into what we now call Old English. Old English did not sound or look like English today. Native English speakers now would have great difficulty understanding Old English. Nevertheless, about half of the most commonly used words in Modern English have Old English roots. The words be, strong and water, for example, derive from Old English. Old English was spoken until around 1100.
Middle English 1100-1500:
In 1066 William the Conqueror, the Duke of Normandy (part of modern France), invaded and conquered England. The new conquerors (called the Normans) brought with them a kind of French, which became the language of the Royal Court, and the ruling and business classes. For a period there was a kind of linguistic class division, where the lower classes spoke English and the upper classes spoke French. In the 14th century English became dominant in Britain again, but with many French words added. This language is called Middle English. It was the language of the great poet Chaucer (c1340-1400), but it would still be difficult for native English speakers to understand today.