In an exemplary embodiment of this invention, corrugated board is folded into a building system. The building system comprises a plurality of blocks and connectors. The blocks are rectangular cuboid in shape. The bottom and top sides of the blocks have rectangular arrays of holes. The blocks may be releasably connected by aligning the top holes of one block with the bottom holes of another block, and then inserting connectors into the aligned pairs of holes, one connector per aligned paid of holes. The ends of the connectors that are inserted are circular or equiangular polygonal in shape. In some embodiments, compression is used to releasably hold the connectors in place.