A possible addition to tale four:
Instead of the current system of land bridges that span the river at various locations to allow crossing, the game would start out with no crossings. Bridges would have to be researched at the universities for the technology to create them and would become area-wide projects.
Bridge examples would be
bridges would have a certain minimum distance between them (so the landscape/river could not be cluttered with an over-abundance of them) however this becomes problematic when the bridge is not being built up or down river but rather along another fork that is within this minimun distance. Travel straight across two might be hindered by the inability to build a second bridge. A solution to this problem is to have only specific sites 'suitable' to build on, pre-set into the game.
Bridges could also be viewed as monuments in the sense of adding 'pretties' to make your bridge better than mary-sue's bridge down the way, thus creating a sense of communal pride and building the biggest bridge or the most elaborate.
To mirror the London bridge history, sufficiently grand bridges could actually support small structures on them (such as obelisques, guild houses, pools, etc)
The underlying purpose of a bridge is to allow for the passage of water-going vessels from one side to the other. Rafts, barges, etc would be able to travel up and down river without being hindered (by bridges, anyway) ;)