Taranis had once hosted an outpost used by the Ancients, which included the planet's Stargate; the Taranians apparently went without knowledge of either until a series of underground caves and tunnels led them to discover the facility. Within, they found a great deal of apparently undisturbed Ancient technology, including a damaged Aurora-class battleship and, more significantly, a fully functioning shield.
While the Taranians were relatively advanced by local standards, possessing personal computers and sufficient knowledge to operate some of the Ancient equipment, they soon recognized that they did not have the ability to repair the Ancient systems should anything go wrong. Therefore, when the shield generators on the Ancient outpost, which had become a place of refuge for many Taranians fearful of the Wraith, began showing problems, they sough to enlist outside help, ultimately contacting the Atlantis expedition. This proved to be serendipitous, as it was soon discovered that overuse of the outpost's geothermal power system had triggered the imminent eruption of a supervolcano that threatened to extinguish all human life on the planet.
With the aid of the Earth ship Daedalus and the Ancient warship, which Dr. Rodney McKay was able to partially repair in time, most of the Taranian people were successfully evacuated, and resettled on another planet with the help of the Atlantis expedition. (SGA: "Inferno")
About a year later, however, the Taranians fell victim to the renegade Wraith known as Michael Kenmore, who used the population in his attempts to breed a new form of soldier based on the Iratus bug. By the time a team, the Expedition's flagship team, First Atlantis Reconnaissance Team or AR-1 was sent from Atlantis to investigate the disappearances, every Taranian on the planet had apparently been killed. (SGA: "Vengeance")
In 2010, while investigating the ruins of Emege on Athos with Teyla Emmagan, McKay realized that the city's shield had run on geothermal energy similar to the Taranian shield and explained to Teyla that unlike the Taranians, the Athoisans had understood the warning and shut the shield down when their supervolcano threatened to erupt as a result of continuous shield usage. McKay noted to Teyla that if the Taranians had heeded the warnings and shut down the shield, the supervolcano would've been fine. (SGA: "The Mysteries of Emege")