Abstract: A construction unit adapted for constructing a retaining wall to keep a bank of earth from sliding or water from flooding, includes a plurality of U-shaped concrete panels having at least one drain, at least two I-shaped concrete panels each of which is connected to the rear end of one of the U-shaped panels, and at least one concrete shelf plate both ends of which are received by shelf receiving recesses formed in the inner surfaces of the U-shaped panels and the I-shaped panels. The U-shaped panels are vertically piled and further include a vertical engagement means to engage with the plurality of said vertically piled U-shaped panels, and connection members to connect to the I-shaped panels. This vertical engagement means includes an upper hole formed in the top surface of a lower panel of the vertically piled U-shaped panels and a lower hole formed in the bottom surface of an upper panel of the vertically piled U-shaped panels, and a steel bar installed in the upper and lower holes.