Nicolock ALT WALL TRAV 16" x 6" Alta Wall Travertine is a beautiful solution for organically partitioning your landscape. This Nicolock retaining wall system uses versatile 6-by-16-inch blocks that are manufactured with our state-of-the-art process. Our single-sided stones feature a hard-split, rock face texture to create functional garden, walkway and hillside walls, underscoring the natural beauty of the landscape. The tapered sides make it easy to build circular patio walls and other curved faces. The hollow core design reduces weight while maintaining structural integrity.