Siege towers, gates and drawbridges

[D B Campbell]

IIRC, not even Baatz's otherwise detailed Town defenses in the Roman West referred to drawbridges.

I think you have your answer, Stefan!

Off the top of my head, I know that the fort of Bar Hill has a continuous ditch cutting across the west gateway, but I think that has more to do with the steep slope on that side. (Stick a gate on that side because the plans say so, but nobody's ever going to use it.)