We can layer columns and modules on top of other colums and modules by using grid-area. Just specify the row-start/column-start/row-end/column-end for each child. You can also use z-index if you want to adjust the child stacking order.

Credit to gridbyexample.com for inspiring this example.

[fl_row] {
    display:grid;
    grid-gap: 10px;
    grid-template-columns: repeat(5, 1fr);
}
[fl_row] .a {
    grid-area: 1 / 1 / 3 / 3;
}
[fl_row] .b {
    grid-area: 1 / 3 / 3 / 5;
    z-index:1;
}
[fl_row] .c {
    grid-area: 3 / 1 / 5 / 3;
}
[fl_row] .d {
    grid-area: 3 / 3 / 5 / 5;
}
[fl_row] .e {
    grid-area: 2 / 2 / 4 / 4;
}

A

B

C

D

E