From Discworld & Terry Pratchett Wiki
The bridge between Treacle Mine Road on the Morpork side and Wharfinger Street on the Ankh side. Like most other bridges over the River Ankh, houses are built on it. It is roof, if not home, to the group of beggars known as the Canting Crew. People traditionally built houses on bridges partly because of the pressure on building land elsewhere in the cities, and mainly because of the quirk in British local taxation law that holds that land tax (rates, business tax, etc.) may only be levied on houses built on... well, land. This has an old and honourable tradition in Britain, and one enterprising builder recently revised the tradition in Scotland by building a combined bridge-cum-house, so as to evade local property taxation legitimately. Misbegot is not an exceptionally wide bridge (or perhaps the unauthorised building over the years has narrowed it) and it may easily be blocked by a haywain shedding its load. In accordance with the law of narrative causality - when the hero is trying to get to somewhere important quickly by a critically important time with only five minutes to spare, his progress will be delayed by obstructions of all kinds - this happens to Sam Vimes at five to six one night.
All bridges over the Ankh (Rimwards to Hubwards)