The bridge is a mile and a half long and crosses the Firth of Forth north of Edinburgh. At the time of its opening in 1890 it was the longest cantilever bridge in the world, and used the highest standards of engineering available.
Its maintenance was immortalised in the phrase 'like painting the Forth Bridge', meaning a never-ending job, but new products and methods mean that the task was finally finished in 2011 and the structure won't need painting again for another 20 years!
You can read more about the bridge, and one of its contemporaries, on the History Anorak website.
