To provide a civil engineering structure useful for constructing roads, building foundations, mountains, or greening rooftops.

A rectangular block 1 of foamed synthetic resin is fixed in place on top of a leveling layer 29 and an upper block 1A is laid on top of the block 1 via a framed joint member 9, with their piled condition provided over a predetermined spread in the horizontal direction as well. Next, a sheet- shaped joint member 9A is fitted into the engaging part 7 of the upper block 1A, like a lid closing the opening of the block 1A, to construct the civil engineering structure. Thereafter, banking 33 is produced on top of the civil engineering structure and trees 34 are planted therein to complete construction of a mountain.