Creating Watchtowers & Forts

[DVX BELLORVM]

Can anyone show me a good screenshot of their use of forts please?
Either Campaign map, or Battle map.

Thanks

This fort is part of my supply line, placed between Constantinopole and Thessalonica...





... and this is how it may look during a siege if the enemy brought his artillery




edit:

Spoiler Alert, click show to read: 

On this screenshot you can see a ring of defensive forts around my capitol Antioch (it's not a greatest screenshot, it was created for some other purpose).
The function of this forts is not to defend the city, but to stop the invading army so I can engage it in the open field. When I built it, I was having a financial problems, earning only a few hundreds FL/turn. Then a crusading army came from nowhere, using it's doubled speed, and besieged Antioch. Since Antioch was my main economic city, I couldn't afford it to be besieged as I would lose it's income. That's why I built the forts around it.
They also proved usefull during the Timurid invasion...