Question: Did London Bridge ever really fall down, like in the nursery song?
Answer: Yes. Quite often. The first London Bridge appeared during the Roman occupation of Britain and was made of wood and clay. It and its successors tended to get washed down river a lot, and in 1091, London Bridge blew down during a tornado, along with six hundred or so houses. The stone bridge started in 1176 survived the Great Fire of London in 1666, but the foundations and arches were weakened and in 1831 it was knocked down and another built nearby. That one began to sink down under the weight of modern traffic round about 1962 and was auctioned off a few years later. Purchased by an American, Robert P. McCulloch, founder of Lake Havasu City, Arizona, it was taken down and reconstructed in Lake Havasu. The current London Bridge seems to be holding up. For now.