El Alamein anti-tank ditches

[Green]

It appears this was actually a deliberate design choice. I found this in the Compass '40 Notes;

"...the Italians were exceptional at creating fortifications.  Italian objectives at Tobruk, Bardia, Sidi Barrani, Nibeiwa and the East and West Tummar had been heavily fortified.  The Italians were excellent diggers and masons and when given adequate time they would turn barren desert into a fortified area.  It is important to note that at Tobruk and Bardia the Italians dug extensive anti-tank ditches.  However, at Sidi Barrani, Tummar East, Tummar West and Nibeiwa the Italians had constructed huge earthen walls that had the same effect as anti-tank ditches. These walls served against the Italians by largely trapping them inside their fortified areas once the allies broke into them. As a design decision, all AT ditches cannot be crossed by infantry units since they represent high walls. This means that the allies MUST take good care of their limited engineer units because these units must be used to blow a hole in these AT ditch / high walls. Keep in mind that at Tobruk, the two bridge hexes can be breached with assaulting Travel Mode units so even if all allied engineer units are somehow lost at that point, it would still be possible (but very difficult) to breach Tobruk at these two points."