London's River Thames has twenty-se

London's River Thames has twenty-seven bridges. But Tower Bridge, the first bridge over the Thames as you travel to London from the sea, is the most famous of them all. What makes Tower Bridge so exciting? Why do visitors come from all over the world to see it?The thing that is surprising about Tower Bridge is that it is open in the middle. It does this to let the big ships through to the Pool of London. If you are lucky enough to see the bridge with its two opening arms high in the air, you will never forget it.On its north side stands the Tower of London itself. Although they look the same age, the Tower is almost a thousand years old, and Tower Bridge is only about one hundred, it was built in the 1890s. By1850, everyone agreed that a bridge across the Thames near the Tower was most necessary. But the designers argued about the new bridge for another thirty years. This took so long because they had two big problems.