Slitherine

I was re-reading Field Fortifications (FF) and Portable Defences (PD), where it says they can only be used if permitted in the companion army book, in particular I was looking at PD,I was trying to think of or find an army that uses PD? one of the obvious candidate would have been Roman caltrops but looking thru Legions Triumphant and Rise of Rome gives no options, so was this rule implemented solely for the English long bowmen or are there other troops that thought it was a good idea to have the odd pointy thing stuck in the ground facing the oncoming hordes??

Western Han for one.