(Given that cutting though the ground is possible, like how quarries are planned to look like, dug deep)
Generic name: Ditch
Specific name: Faction specific
Phase: Town phase
Construction Cost: Food (Labor) - high food cost
Takes time to build one (Like walls)
Infantry can walk though (like farms) but are slowed down
Can only be destroyed (dug) by infantry
Impassable to siege equipment (Because battering rams suck and I don't like them, haha)
Common Iron age defensive construction, both Romans and Celts built them together with their walls (It might be nice to make siege warfare more interesting in 0AD)