Empire Builders: Big-Time Hollow Blocks for Big-Time Blocksters. An empire is only as strong and sturdy as its foundations. Kids can build some mighty strong and sturdy empires with these large hollow blocks. Each block weighs from 1 - 3 lbs so children can maneuver them easily, arranging and stacking in various ways to build forts, castles, playhouses, and all kinds of other magical kingdoms. Each piece is constructed of sturdy hardwood (9- to 11-ply) and solid birch, securely glued, and features a smooth natural finish with rounded edges for safety. They're great to use by themselves, or in combination with our Block Sets. Imported. Lifetime Warranty.