The Romans invaded Britain in AD 43 under Emperor Claudius and established control over much of the island. They built towns, roads, and forts, introducing Roman culture, language, and governance. The most famous Roman settlement was Londinium, now known as London, which became a major trade center. Roman rule in Britain lasted nearly 400 years, leading to significant changes in agriculture, architecture, and society. The Romans constructed impressive structures like Hadrian's Wall to defend against northern tribes. However, by AD 410, the Romans withdrew their troops, leaving Britain to fend for itself and marking the beginning of the post-Roman period.