Let me clarify the portal for a minute. It is fairly large, but, as Aersilae indicated, not so large that they can afford to bring through huge weapons of war, at least not yet. Rumor has it that the Demon Lord is working to enlarge the portal, but no one knows how successful these efforts have been. And while Aersilae and Jurai have both seen the portal in action and know what it is capable of, neither of them have any idea how it works. They don't know what is powering it, how the demons are keeping it stable, etc. That is just something they will have to find out.