Did I say that it was a Creo attuned aura? ^^
It was part of my main scenario : five gates in Europe (one in Oslo, one in Scottland, one at Leczyca, one in Bologna and one in La Rochelle) which were build by powerful arch spirits of the magical realm followers, many centuries ago. The archmaga fled the Schism, and she discovered while hiding in Bologna amongst the students, the door of Creation under the city, where she settled the Cult of Taranis, the new house of Diedne.
In fact, all this story started like that:
They received the visit of a dying bjornaer magus who asked them to go with an archmagus in a fortress in Scottland, helping 4 new gauntleted magi captured by some hedge wizards during a quest to find clues about Davnalleous whereabouts.
And during the rescue mission, while going by the backdoor, the PCs had discovered the door of Knowledge. They were happed by the portal and inside, they discovered Daman Allaidh, who has been trapped in a temporal prison for four hundred years. Rather than letting the magi leave, he used them and send them in the future, in Mongolia, where the shamsn of Kubilai have designed a ritual to open temporal prisons. (the scenario was set around this idea)
His future himself - free of his prison by the said ritual, quickly noticed the PCs weren't in their right time. He gave them the key to open his own temporal prison and said to them: "I can say the secret for you to come back to your time", and put a bait: he faked his objectives were : 1- the magi put a strange bag in Durenmar library [a gunpowder pile] and 2- they steal the columbae robe from Prima Ex Misc.
Thinking those two objectives were his only ones, they tried to figure how to double him... they did put the gunpowder in the library, and Dav' (as they nicknamed him 
) made it explode, while, meantime, he cast dragons from the east on Durenmar burning and many magi dead in the explosion of the tower.
After that evenement, the PCs thought "it's only the future, it doesn't matter!" and accepted to do the 2. Since it was the future, they could change it.
But Damhan Allaid didn't care, "because it's only future".
They went back to the fortress - named Stangtiskar = the scar of blood - and went to Stonehenge.
Damhan Allaid said to them they had to do a ritual with 50 pawns of vis, following mongolian texts (yes, the PCs did learn mongolian during the years (3 !! ) they were under Kubilai reign. Did I mention they met Marco Polo?). The mongolian texts were not perfectly read by the Pcs (they had too much and not enough time, since each year they were in the future, their magical abilities decreased, something Dav told them it was "because they don't belong here" - which was true) and they followed futureDav advises.
Back to their time (because the ritual 1 was correct), they had to do a second ritual to "anchor" themselves in their time. And that was the trick. Doing the second part of the ritual - they didn't have doubts about it, they have doubted the 1 but since it worked, they felt for the "Damhan was stupid, asking us to change something, but in our future" explanation (yeah, it's easy to underestimage someone ^^).
And by the second ritual, they freeed PresentDav.
And it's with fear they realised, one year later, they weren't anchored... 
Damhan goal was not to kill the PCs, and he initiated negociations with the Order of Odin, to declare a war against the Order, expansionnist bastards (IHO, it's right! they forced england and scottland magi to die or join!). And during 1 year of play, he tried to corrupt PCs...
I succeeded to convince the Criamon to rejoin my cause, and he started acting as a spy, giving the NPC informations. And that answer the question "why does Dav always know what we are doing" that they asked themselves so much during the sessions 
. Yeah, you had a traitor! Blame Navius!
Eventually, they got access to the Door of Change, in oslo, they discovered the Door of Destruction in Leczyca, and the Tremere ally's redcap Richard went in Bologna, trying to discover the door of creation.
Did I mention that between the PCs, one was of Tremere and his parens had his own agenda (use the doors to go in the past and kill Diedne immediatly after the Founding?) and another was Jerbiton, and due to issues, he owned the Primus Andru a service... and he started to act as a spy on the Tremere. Andru wanted to use this portal to counter Tremere plans... thinking the Tremere were trying another Coup d'Etat and envisaging another Sundering.
So we had, amongst the PCs, two who played most of the sessions spying on themselves and keeping informations for themselves (they failed many discoveries because of that!) and one double spy (the criamon was working for the Jerbiton, but the Tremere thought he was working for him, but,in fact, he was betraying all of them to Damhan ^^).
(For the story, the Jerbiton player's companion was the redcap allied to the Tremere... who spoke about mindfucking?)
Ah and for the good end, the plot for the first adventure was easy: the 4 "young magi" had received clues that Damhan was still alive. Guess who send it? Yes, the PCs who because of the ritual, came back 1 year before of their departure! They had to set up this story to "re anchor" themselves in the timeflow. Had they failed this, they would have ceased to exist after a decade or two. Because their magical power was leaving: -10 to all rolls by year, and +10 to longevity by 5 years.
It was a really interesting story, and I liked every moment of it.
The discovery of each portal was climax, and the (apparent) destruction of the fifth portal in Bologna [as Morgane, the Diedne new archprima had duplicated it and put rumors on the fake portal, of course!] led them to think that they were unusable.