An extension for set number eighteen (18A) includes 230 stone blocks in the three standard colors; brick red, natural sand, and slate blue. The Designs for Architectural Models booklet includes ten building plans for large and complex buildings including a Roman basilica and a stable with coachman's rooms. Packaged in the traditional wooden box for storage with a packing diagram and construction templates. This expansion allows you to build the largest and most complex models. This set plus the combination for set #18 becomes the equivalent of set #20 and allows you to build all of set #20 models.