Nicolock ALT PRO GC 18" x 8" Alta Wall Pro Granite City will reinforce its beauty with functional grandeur. The Alta Pro is a bigger version of our popular Nicolock Alta Wall with blocks that are 2 inches taller and wider. This allows for expansive tiered retaining walls, garden walls, elevated seating areas and more. A rear lip connection system keeps the single-sided wall system secure, while a one-inch setback per row offers a solid angle for preventing erosion on hills.