Here is how the regular pentagonal fort looks from the ground 1 km away from the center. I have developed the emplacements for cannons only on one bastion.

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1: That is the fort?
2: Yeah.
1: That tiny thing over there?
2: Yup that tiny thing over there.
1: It's too low, even I could bring a ladder from home and scale it.
2: It may seem very low from here but that over there is a 6 meter wall over the ground (glacis) and there is a trench 10 meters deep and 30 meters wide before you can reach the wall, and that trench is also in the range of the defensive artillery.
1: ... and no big walls to shoot at with my artillery... It's not fair!
2: That's the purpose.

Now you may tell me "Hey 4maram, why not just copy and paste the polygons on the other bastions?". Well, Sketchup is a bit of a ... . You can't draw perfectly regular polygons here. You have to paint every single line, because, while the bastions may seem like the same, they aren't.
Well, I end my rant against the SketchUp program here (for now...).