A fun bit of hydraulics: London's Rolling Bridge.

Its probably not particularly difficult, but I thought it was pretty cool looking.

Unrolling

Rolling up

My guess is the 14 pistons are in pairs to form seven proportional control axises. Even though the piston motion appears to be linear the loading is not - that's what makes it interesting.

Seven articulated cylinders would not be easy to control. The gains must change on the fly as the gate curls up. With a little math one can compute how the gains will need to change.