I imagine it's straightforward but I thought it sensible to check. The wall is two bricks thick - the exterior side is 6ft and reaches the ground while the interior is 4ft and reaches the garden ground level. I intend to dig down 3ft to install steps to a gate which will be 965mm-wide cut into the wall. I don't think this will need a lintel, but I want to check whether any additional support will be necessary.