Pulteney Bridge
Bridges across rivers are obviously a means of transit but someone has to pay for them to be built. Often bridges would be built by local landowners at their own expense simply as a means of shortening their own journeys. Othertimes the bridge would be built as a privately-funded "toll bridge" with the entrepreneurial builder looking long-term at his (usually his, as opposed to hers) investment to provide a steady income into retirement
Modern bridges are obviously part of the transport infrastructure and so are government commissioned and usually paid for from general taxation, or, as with some here in the UK, by contracting out to private enterprise who then set tolls to get their money back (with a profit of course!).
Bath's Pulteney Bridge is an interesting one to research. William Johnstone Pulteney, seemingly a shrewd and canny Scotsman, married into local money and became the landlord of the village of Bathwick and its surrounding rural estates. Bathwick, being across the river, was at the time only accessible from the City of Bath by a small ferry.
Pulteney, with his eye to developing his new wife's estate as part of the burgeoning Bath, decided to commission a bridge. Following consultation with the Bath City Council he engaged a local architect, Richard Adam (and brother) to put together a plan.
The Adams brothers were great fans of the medieval idea of building bridges which would pay for themselves by hosting shops and dwellings. This idea of course appealed to Pulteney's Scottish frugality and so the bridge was duly constructed with rows of shops on each side and with attic dwellings above them.
Bridges of this type had been built in many European cities but in most cases with disastrous consequences. The bridges were often washed away during flooding and obviously so too were the businesses and houses. This made Pulteney's bridge initially a bit hard to let, there being plenty of solid dry land on now the other side, but by all accounts he did succeed eventually in selling the leases.
The inevitable did happen though. In 1799 one of the piers was swept away and the following year the other, resulting in the bridge becoming more of a ruin than an asset. Not to be deterred though, Pulteney had it rebuilt and whilst it became a bit of a ramshackle developement at least it was still there.
In 1936 the bridge was declared a National Monument and by 1951 was pretty much restored to its present condition.

Prior Park Landscape Garden
Great buildings
A Taste Of The Chaos!
The lovely ruined wall