> There are three basic types of draw bridge. The most common is the kind where one or both sides rise to a near vertical position allowing a tall ship to pass.
>
> Sometimes a section of the bridge is on a turntable so that it can rotate 90 degrees allowing ships to pass on both sides.
>
> Another type of drawbridge is the vertical lift where a section between two towers rises high enough to allow ships to pass underneath. The Tower Bridge in London is one of those.
>
> Without draw bridges, Hollywood car chases would be a lot less interesting.
> Howard

Tower Bridge fits neatly into the first category. I think a vertical lift might have been a challenging feat for engineers in 1870. Most such bridges were built comfortably into this century.

Also, when I hear the term "drawbridge", I immediately think of a bridge across a moat, protecting a castle from attack, rather than a roadway across a river. I suppose that goes back to school history lessons.

wintermute