Abstract: An improved structure adapted for undersea construction is described comprising a plurality of foundation blocks, each foundation block comprising a rectahedral parallelepiped opposite faces of which are concave and convex, respectively, the opposite faces being sized and shaped to interengage matingly, such foundation blocks being interfitted into a three-dimensional array; a plurality of base pad units supporting said foundation blocks, each base pad unit comprising a rectahedral parallelepiped one face of which is convex, the opposite face of which has a plurality of protruding lugs, and the intermediate faces of which have T-shaped slots extending the length of each side, such base pad units being interfitted into a two-dimensional array by means of I-shaped keys which fit into adjacent T-shaped slots; a plurality of leg blocks supporting said base pad units, each of said leg blocks comprising a rectangular parallelepiped one face of which is convex, the opposite face of which is concave, the opposite fac