Thanks!!
These stakes are absolutely brilliant! I don't know why I've never even noticed them before!

The only problem is, how to make the enemy attack you once the stakes are in place.
And also, I didn't think my own cavalry would have to be routed around them (silly really) and had half my unit of mailed knights decimated when I gave them the order to return behind my longbows after dealing with some French crossbows.
"What's that? Stakes? They're OUR stakes, men! Charge!.. Run away, run away..."

Still, can anyone answer my question about battle map styles?