I dont know if it was mentioned in any of those links your guys put up, but the most impressive bridge documentary is this one on the leonardo project. They started off by building a partially wooden pedestrian bridge using Da Vinci's design. A second one is being made using all stone... this one might be for traffic too...
Since I dont knwo alot about this stuff, all I can say is that the bridges use converging arches to perform the loadbearing with another arch as the roadway... beautiful....
<url>http://www.vebjorn-sand.com/thebridge.htm</url>