This is the second piece of Martian terrain I've done with the first being the farmstead. It's certainly a large model and at the moment it's only a third...
As stated, the toll towers are tall, single structures with an attached small temple and are generally 'owned' by a single family.
The construction for this was the same for as the farmstead building but obviously on a grander scale, I was wanting to give the impression of an imposing structure and I think it worked. The ramp goes up to the reverse drawbridge and the passage goes through to a similar drawbridge on the other side which leads onto the bridge proper. The bridge and second tower still need to be made and when I'm better I'll make a start (after Christmas probably).
I'm am working on designing a vertical ballista that the City Martians use for defence and we are also hopefully near to having the first City Martians ready for release.
I'll leave you with some pictures of the first toll bridge tower...