Down-Scaled Fortifications
Especially if the fort to be built was intended for a small area with few soldiers to hold it, the basic pentagon design was too much. For scaled-down fortifications, four bastions (or even three) worked sufficiently.
These three fortifications were in the Low Countries. Note in the bottom two use of available waterways in place of digging a moat all the way around. Note also the simple bridges in front of the main gates. (Two appear to suggest little drawbridges.)