(If I might break character for a moment:
Johann, MoW's character (Galipus) didn't say a word about the Romans out loud, he thought it.
And the puddle's on the wall, like a door.
Macky, your character had a prophetic dream involving a snake, right?
I threw in the whole "serpent shrine" thing for your character, so go wild.)
The rest of the party watched Marius Gaius run boldly at the puddle on the wall.
When he neared it, he started fading from view until he became completely invisible.
The only sign he had entered the puddle was a big ripple coursing through the substance.
Gale sighed, "I thought so."
"Thought what?" one of his team asked.
Gale began to stride forwards, speaking as he went.
"It is a portal, to the dark world. Judging by its appearance, it leads to a mirrored version of this room."
He paused, "Well, actually, it's probably not mirrored at all, the portal here just...nevermind."
He continued walking, "However, I know what happened to Gaius.
With this kind of teleportal, you fade away as you approach it, and reappear on the other side once you've made enough distance.
Basically, you don't actually enter the portal at all, you just perceive yourself as doing so. With me so far?"
Everyone in the party shrugged.
"Yeah, I know, it's confusing. It took me ages to get it when Lasinus explained it to me.
Suffice to say, we can safely enter this portal."
"Now, who wants to go first? After Gaius, I mean.
...Nobody? I'll go first then."
Gale continued striding towards the portal.
As he neared it, he felt no difference in himself, but he knew he must be disappearing.
Upon reaching the portal, he stepped through (or perhaps just thought about it), and felt...no change whatsoever.
However, everyone was gone, save for Gaius, who had reappeared some distance away in the form of...
"How can you find so many ways to annoy me, Roman?" Gale muttered. "You look like the good god Horus."
As Gale walked forward, he began to reform, into a monstrous demon with skin of stone.
On his back, a complex tattoo blazed brightly.