London is a big city, with a history that goes back to ancient times. London was founded in 43 AD, when the Romans built a trading port on the river Thames near where London Brige is today. They called it Londinium, and made it the capital of the region of the Roman Empire called Britannia. Towards the end of the seventeenth century, two tragedies struck London. The Great Plague, and the Great Fire in London. The Great Plague was a terrible epidemic that broke out in London in 1665.