Today, we are going to explain how and why Allan Block retaining wall blocks stack together. The basis of stacking blocks that lock together give a wall system the structural component and Allan Block is no different. Most Allan Block’s consists of a front lip and bottom notch. As you place a second block on top of the first, the bottom notch of block #2 (top block) interlocks with the top notch of block #1 (bottom block) which engages the system. This type of system is the same for ABCollection, AB Europa, and AB Aztec collections. AB Fieldstone has the same type of interlocking system, but the anchor unit has a rear lip and notch system. These blocks stack the same as all other blocks, but the back lip of the top block (#3) interlocks with the notch on the bottom block (#4). All Allan Block products lock together with a lip and notch system, which makes Allan Block one of the easiest products to use.