In 55 BC Julius Caesar (ca 100–44 BC) invaded Britain, but the real conquest of the country took place in the years 43–47 AD under Emperor Claudius (10 BC–54 AD). One of the first things the Romans did was involve the conquered tribes in the administration of the province. The Romans encouraged the growth of towns near their army bases and established special towns as settlements for retired soldiers. They persuaded the ruling class of Celtic aristocrats to build town dwellings, and they turned the towns into centres of vibrant commercial activity. Town boundaries contained a regular network of streets. Most towns were surrounded by stone walls. The centre of a Roman town was the forum which gave access to the basilica, or town hall. It was here that courts of justice were held, though it could also be used for merchants’ assemblies. Every town had public baths. They were open to both sexes, though at different times of day, and served as a healing spa and meeting place. Roads joined the towns together. The Romans built over 9,600 kilometres of roads in Britain. They weren’t always straight, but they were amazingly well built and made troop movement, and later the movement of commercial goods, much easier. Possibly the most important monument built by the Romans in Britain was Hadrian’s Wall, constructed as a defensive fortification and customs barrier from the east coast to the west coast between England and Scotland. The beginnings of London can be dated to the invasion of the Romans in 43 AD. A bridge was built across the River Thames. This first ‘London Bridge’ proved a convenient central point for the new network of roads which soon spread out like a fan from the crossing place. The Roman settlement on the north side of the bridge, called Londinium, quickly became important as a trading centre for goods brought up the river by boat and unloaded at wooden docks by the bridge.