T-Walls - What are they anyway?

I know I mentioned T-Walls in previous posts. Some of you may not have had the privilege of ever seeing one, so I thought I should explain and provide pictures. As you can see, most T-walls are about 10 feet tall, with a wider foot forming the cross-bar of an upside-down "T" - hence the "T"-wall. The sides are notched so the walls fit together side-by-side without a gap. Entrances are formed by offsetting T-walls and leaving a gap to walk between. The walls are used for protection around all buildings/structures on our bases, to form security walls, and to line roads and neighborhoods in cities. They are what we see everywhere...miles of plain, gray concrete. At least the Iraqis paint elaborate murals all over theirs - much better.