Hollow Clay Bricks

A long time ago, the only thing that would keep a home warm was fire. Without fire, homes were made of wood and clay bricks, both of which were incredibly flammable. But the clay bricks had a unique quality. The bricks were made from a mixture of clay and sand, with a natural polymer in the mix. This polymer would actually melt when the bricks reached a certain temperature, and this made the bricks waterproof.