A cell for a stormwater management system adapted for retaining or detaining stormwater. The cell comprises a body portion and an internal region. The body portion comprises a plurality of corner columns spaced from each other, a plurality of wall portions, and a window. Each wall portion extends from one of the corner columns to another of the corner columns. Each wall portion comprises an inner surface and an outer surface. The inner surface of each wall portion is curved. The window is through at least one of the wall portions. The window is adapted to permit passage of stormwater into and out of the internal region of the cell.