How to make matrix elements which spans multiple columns/rows?

I have a matrix which I would like to typeset. From the linked image, it can be seen that the bottom elements span 2 columns (and 2 rows but that’s not as important), how do I typset it?

Right now I am trying this

begin{gather}
    begin{bmatrix}
        0 & 0 & 1 & 0
        0 & 0 & 0 & 1
        A^{-1} C & & -A^{-1} B
    end{bmatrix}
end{gather}

but it doesn’t seem to work, as expected.

documentclass{article}
usepackage{amsmath}
begin{document}
    begin{gather}
    begin{bmatrix}
    0 & 0 & 1 & 0
    0 & 0 & 0 & 1
    multicolumn{2}{c}{A^{-1} C} & multicolumn{2}{c}{-A^{-1} B}
    end{bmatrix}
    end{gather}
end{document}