Why can't take these arty units ?

[NicolasBourbaki]

Is the optional rule Movement Threat Disorder checked?

Yes.

But 500+ men should be able to take a few guns ...
I sacrifised at least 5 or 6 units, most of them of 400+ men ...

Also, by looking at the 3D map (i'm normally not using the 3D map) I notice that the arty units are in a fort !!! This may explain too of course. Somehow ...

These Prussian arty guys definitely need a decoration !