Roman Bridge - Reference pics

[DevinNight]

it's interesting that they didn't have both sides of the drawbridge firmly rooted to the bottom of the river, instead the one side is being held up by boats and held in place by a stone pier a bit up river.

[Talroth]

it's interesting that they didn't have both sides of the drawbridge firmly rooted to the bottom of the river, instead the one side is being held up by boats and held in place by a stone pier a bit up river.

This is part of the pontoon design. As someone else said the pontoon bridge will rise and fall with the water level in the river. By allowing an overlap between the draw bridge and the pontoons you reduce the effect of water level change, thus killing two birds with one stone. You get a drawbridge to allow boats to pass, and a variable flex point to deal with the water changing.

It also allows you to pull the whole bridge out if it is at risk of ice damage during the winters, or heavy flooding damage in the spring. Not to mention, as someone else said, you can untie the whole bridge and pull it to your side while defending.