London is an old city. It grew up around the first point where the Roman invaders found the Thames narrow enough to build a bridge. There has been a "London Bridge" in the same area ever since. They founded a Celtic settlement then known as Londinium and later they had turned it into a large port and important trading centre with a long wall of stone and brick. Inside the wall low houses were built with bright red tiled roofs. The Tower of London was founded by JuliusCaesar and in 1066 rebuilt by William the Conqueror. It was used as a fortress, a royal residence and a prison. Now it is a museum and also the place where the Crown Jewels are kept. Time passed. London grew and became a great city. The coming of the railway changed London for ever. The first underground railway was opened in 1863 between Paddington and the City. Today London is the capital of Great Britain and Northern Ireland. It is one of the most beautiful cities in the world. There are many places of interest in it and this city is well worth visiting.