In 55 BC the Romans pushed into Britannia, where the Celts lived. Roman military rule lasted there until about 400 AD. The Romans built a great wall across the narrowest part of Britannia to hold back the warlike northern Celtic tribes. In the south, however, the Roman occupation was peaceful, and many of the southern Britons adopted Roman ways and learned the Latin language.

During this period the Romans also had regular contact with Germanic tribes on the European continent. When the tribes later invaded Britain, they brought with them several hundred Latin words they had learned from Roman influence on war, trade, and everyday life.