1) Low Greek pillars 
• (pl. ) of Cippus
These obstacles were long pits, trenches, or fossae, 5 feet (1.5 m) deep, perhaps with a W-like profile, inside which were fixed obstacles of sharpened tree branches. 
obstacle trenches These were long pits or fossae, 5 feet deep, perhaps with a W-like profile, inside which were fixed obstacles of sharpened tree branches; they are described by Caesar (De Bello Gallico, VII.73-80).