Here's why:
* The year 523 AD is around the time of the Anglo-Saxon invasion of Britain. The language spoken by these invaders was Old English, a Germanic language very different from Modern English.
* Old English had a completely different vocabulary, grammar, and pronunciation. Think of it like a different language altogether. Words like "morgen" (morning), "steorra" (star), and "heofona" (heaven) were common.
* Old English was heavily influenced by Old Norse, due to the Viking raids and settlements in England. This influence can be seen in words like "skull" and "knife".
* The Norman Conquest in 1066 AD brought a massive influx of French words into English. This marked the transition from Old English to Middle English (around 1150-1500), which is still quite different from Modern English.
So, to answer your question more directly, 1500 years ago, people in Britain were speaking Old English, a language almost completely unintelligible to modern speakers.
It's fascinating to think about the journey of the English language and how much it has evolved over the centuries!