Masonry arch bridges are an important part of the British road and rail network. There are for instance, about 40,000 road bridges, about 40% of Britain's total bridge stock. The amount of traffic they are now called on to carry has increased enormously since they were built, as has the weight of some of that traffic. Although these bridges have been in existence for thousands of years, research on their structural behaviour is still being carried out and new analytical techniques are being developed.