An abandoned Ancient city on planet Proclarush, virtually identical in design to the Atlantus outpost discovered under the ice of Antarctica on Earth. Taonas housed an Ancient star map and at least one active Zero Point Module, which powered its systems until SG-1 took it back to Earth.
Proclarush Taonas was one of the first cities built by the Lanteans (the Ancients) as they colonized the Milky Way Galaxy. But it was eventually abandoned when the inhabitants learned that their sun was nearing the end of its life.
SG-1 eventually discovered part of the city beneath a protective dome, formed during a period of extreme volcanic activity. With the dome compromised by SG-1's visit and the planet overcome by ongoing volcanic activity, is is likely that Taonas has been destroyed.
Lost City, Part 2 - His mind under the control of Ancient knowledge, O'Neill identifies the outpost on Proclarush as "Taonas."
The Pegasus Project - Disguised as a Lantean hologram, Morgan Le Fay speaks of the history of Taonas and its evacuation.