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Previous Thal settlements
The original settlement of the Thal Republic (AUDIO: Corruption) was reduced to little more than a dome by the Thousand Year War against the Kaleds. After the Thal's neutronic missile brought down the Kaled Dome, Davros unleashed the newly-created Daleks into the Thal Dome as the Thals celebrated victory. The Daleks caused yet more death and destruction before they were recalled to the Kaled bunker and sealed inside by Bettan's resistance movement. (TV: Genesis of the Daleks) In the distant aftermath of the war, a group of Thals embarked on a perilous journey, hoping to reach the ruins of the Thal Dome and resettle. However, the Daleks had occupied the ruins and slaughtered the only two survivors. (COMIC: Safe Haven)
Occupation of the Dalek City
Over the centuries, the Daleks rebuilt the Kaled Dome into the Dalek City of Kalaann, (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe) while the Thals had became a peaceful race and struggled to survive in the wastelands of Skaro. Aided by the First Doctor, Susan Foreman, Ian Chesterton and Barbara Wright, the Thals learned to defend themselves and raided the Dalek City, cutting off the Daleks' power supply. As the City housed valuable Dalek technological equipment, food and water supplies and the means for effective agriculture, the Doctor suggested that the Thals move in. (TV: The Daleks) Unknown to the Thals, however, some Daleks survived in the hidden incubation level beneath the rest of the city. (AUDIO: Return to Skaro)
The Thal City
However, subsequent generations of Thals ultimately decided to build their own city, not far from the site of the Dalek City and the petrified jungle. The close proximity allowed scientific research teams better access to city during the construction of the new Thal City. As a result, the new Thal settlement closely resembled the Dalek City. The Thal Council formed the governing body, led by the High Leader of the Thals.
The Thal's chief scientist, Tryana, eventually made contact with the surviving Daleks during one expedition to the Dalek City. The Dalek Supreme offered to aid her in the reconstruction efforts. Successfully manipulated, Tryana accepted and provided the Daleks with power from the Thal City, but she kept her correspondence with the Daleks a secret. Much of the city's features were built with technology provided by the Daleks, most notably the ionisation towers which reduced the radiation in the atmosphere. The Daleks built a secret tunnel connecting the two cities, which Tryana was not made aware of. (AUDIO: Return to Skaro)
Assault by the Daleks
Fifty cycles after the Thal-Dalek battle, the Dalek Supreme launched another attack against the Thals. Using the secret tunnel, the Daleks hijacked the ionisation towers and used them to discharge electricity into the streets, killing many Thals. This was followed by a full assault by a new Dalek army. With the assistance of the First Doctor and his companions once more, the Thals regained control of the towers and forced the Daleks back to their own city.
Ian and the Thals boosted the power being fed from the Thal City to the Dalek City, overloading the latter and destroying it, along with the Daleks. Victorious once more, the Thals began working to recover but resolved to be more vigilant lest the Daleks return. They noted the possible existence of other Dalek settlements on the planet. (AUDIO: Return to Skaro)