There are 5 London Bridges and each has its own identifying Bridge Mark… together these 5 bridges form the Bridge House Estates.
The Bridge House Estates is one of the oldest operating organizations anywhere on the globe. Founded by the city of London in 1282, the Bridge House Estates grew to be very profitable, charging significant tolls to anyone who wanted to cross the Thames. As the Bridge House Estates accumulated wealth, they expanded and created new bridges. The 5 London Brings are named: London Bridge (the oldest, 1282), Westminster Bridge (1862), Albert Bridge (1873), Tower Bridge (1894), and Millennium Bridge (2000).
Each of the 5 bridges has a unique, symbolic, hidden mark engraved on a secret spot, or affixed to a flag, or possibly carved onto a plaque. Hunting to find these important markings can easily become an obsession. The first Bridge Mark appeared in 1674 on the initial London Bridge. This makes sense. The late 1600's were the height of the Enlightenment, resulting in the formation of several secret societies whose members met to discuss radical new revolutionary ideas. One such secret society (dubbed an "invisible college"), was formed in 1663, and was called "The Royal Society of London for Improving Natural Knowledge," aka the Royal Society of London. Their motto was 'Nullius in verba' which means 'take nobody's word for it." They believed that all facts must be proven by experiment. Sir Isaac Newton was a Fellow of the Royal Society of London. On April 29, 1756, Benjamin Franklin was elected a Fellow of the Royal Society of London. Franklin's kite experiment, proving that electricity is found in lightning, was conducted through the Royal Society.