But, though the Tower Bridge is so remarkable a structure you must remember that it is only new. The most celebrated bridge in London, perhaps in the world, is called London Bridge. It stands next above the Tower Bridge. Two thousand years ago there was no London; where the houses are now were then forests and marshes. Some seventeen hundred years ago the first London Bridge was built; it was rebuilt afterwards more than once; but no second bridge was put over the River Thames to connect the north and the south of London until a century and a half ago. For all those centuries there was one London Bridge. By means of this Bridge the traffic of the south of England crossed the Thames to the north. But London Bridge stopped the ships coming up from the sea and prevented them from going further into the land, because in early days men could only build small arches for a bridge, and these were neither broad enough nor high enough for sea-going ships. So it was that London grew round London Bridge, for here was not only the lowest bridge on the river but also the most inland point to which sea-going ships could ascend. It was an important place, therefore, both for land traffic and for water traffic. [Sidenote: 9. The Tower of London.] On the north bank of the river, a little below London Bridge, the Kings of England in old time built a fortress to defend the town, and also to keep its population in order. This fortress is still standing, although against modern weapons it would now be useless. It is known as the Tower of London, and is a very interesting old place, quiet and silent amid the noisy metropolis around. The King’s Crown and Coronation jewels are kept here. [Sidenote: 10. The River below London Bridge.] The Tower Bridge is so called because it crosses the river beside the Tower of London. Here we have a view taken from London Bridge, looking down the busy river to the Tower Bridge. You can just see the Tower of London on the left hand. [Sidenote: 11. Plan of Greater London.]