Emacs: How can I easily create a new window that spans two existing horizontal windows?

I often have an Emacs frame that is partitioned into two windows like so: ``` -------------------------------- | | | Window 1 | | | |------------------------------| | | | Window 2 | | | -------------------------------- ``` Then I find myself needing a long vertical window that runs the entire height of the frame, like so: ``` -------------------------------- | | | | W'dow 3 | Window 1 | | | | | |--------------------| | | | | | Window 2 | | | | -------------------------------- ``` However, using C-x 3 it's only possible to split either Window 1 or Window 2. The only way to create the long vertical Window 3 is to start again with a single window filling the entire frame, and split it horizontally (then split one of the windows in half again, vertically). This is annoying. I guess what I'm looking to do is to split the entire frame, rather than just the active window. I've Googled for solutions, but without success. Is it possible to create a new window that runs down the entire length of an Emacs frame, regardless of any windows that already exist inside it?