Talk to Raminus after your promotion to Evoker and he will ask you to help another mage, Irlav Jarol, with his excavation and investigation of the Ayleid ruin called Vahtacen. Irlav is somewhere in the Arcane University, so follow your quest marker to track him down and he will direct you to talk to Skaleel, the mage running the research at Vahtacen. Before you arrive at the site, make sure you have a spell, scroll, or staff capable of casting a Frost Damage spell. Travel to the site, south of Cheydinhal, and talk to Skaleel. She tells you that a pillar is blocking their access to the rest of ruins and tasks you with figuring out how to open it. Denel, another mage, is in the room containing the pillar and he suggests that you get a book from Skaleel on Ayleid translations so you can interpret the inscriptions on the four tablets in the corners of the room.
Talk to Skaleel again and she will give you the book. Go back to the pillar room, read the inscriptions, and then talk to Denel again. It turns out that you have to cast four different kinds of magic spells (Fire Damage, Frost Damage, Damage Magicka, and Fortify Magicka), in that order, on the pillar to make it open. You should have brought a Frost Damage spell with you and there are scrolls for the other three types of spells in the chest that you find in that room. Cast the spells in the sequence listed above and the pillar will open up, revealing a stairway. Explore the ruins, killing off the undead that you find there, until you locate an Ancient Elven Helm. Talk to Skaleel and she will instruct you to go back to the Arcane University with the helm. Take the helm back Irlav and then talk to Raminus to receive your promotion to Conjurer.