The Romans first entered Britain in 55 BC under Julius Caesar, although they did not begin a permanent occupation until 43 AD, when Emperor Claudius sent a much better prepared force to subjugate the fierce British Celts. Despite a series of uprisings by the natives (including that of Queen Boudicca, or Boadicea in 61 AD), Britain remained part of the Roman Empire for almost 400 years, and there was a substantial amount of interbreeding between the two peoples, although the Romans never succeeded in penetrating into the mountainous regions of Wales and Scotland.