The dirtiest Roman Fortification trick in my book was to build a berm up that was set about 50 feet out from the actual wall. A 10 foot gap in the center of that berm was covered with moss over a branch lattes with the bottom filled with spikes.

Basically it was a spiked pit trap that ringed the battle field outside of the fortified camp. When the enemy would attempt to storm the walls, they would run up a berm, and most would fall into the pit and die on the spikes, the remainder was then picked off with arrows and javelins.