When I was genning this world, instead of saving automatically I decided to look around the map first. To my surprise I found that an island to the far east was cut off from the mainland by a single region tile at a few points. I knew what I must do.
My determination was reinforced when checking the civilization screen on embark, according to it the island was inhabited by only dwarfs. I took this to mean that it had never been explored by anyone as dwarfs always show up on the civ screen.
Next came the design. How was I to build my intercontinental bridge? A straight line was ruled out by the geography of the area, a diagonal would be far too boring. With the help my my good friend MS Paint I came upon a nice gentle curving design that was easy on the eyes.
Material choice was decided by the land which yielded clusters of bauxite and magnetite along with layers of siltstone and gneiss. When doing my calculations I found that I had just enough stones in the two clusters to make the floor of my bridge. This resulted in the checkerboard pattern that comprises the bridge. Inside the magnetite cluster was a vein of native platinum, this was used for the stairs.
All in all it took five miner/masons, four farmers, eight dedicated haulers and ten dedicated masons seven years to prepare and place every one of the over 3500 blocks that comprise this bridge.
http://mkv25.net/dfma/map-6233-salveages