Great City of the Exxilons

Great City of the Exxilons was the pinnacle of the Exxilon's development and one of the 700 Wonders of the Universe.

Technology
The Great City of the Exxilons was a massive white building, geometrically designed and similar in appearance to the pyramids of the Aztecs. In the centre of the city was a tower with a glowing beacon which was its source of power. In the centre of the city was the control centre, which had power over the whole city. It had no visible windows or doors and had sealed itself up after its creation.

The City was filled with traps which would kill anyone who was unintelligent. Anyone who was less intelligent than the City itself would be destroyed, and anyone more intelligent would have their mind scanned. Underneath the City were root-like structures which hunted by sonar and killed any trespassers. If these methods didn't deter intruders, the City could also produce humanoid Antibodies.

The City was able to absorb all the energy from its surroundings, allowing it to perpetually repair itself. This meant that all technology more advanced than bows and spears would fail, including technology as advanced as a TARDIS. Because of this, the City looked new, even after thousands of years. It also produced a mild electric charge which repelled dirt and grime. (DWN: Death to the Daleks)

History
The Great City of the Exxilons was created by the Exxilons in order to show off their power and skills. They constructed it with all their technology. They designed it so that it was intelligent and was capable of repairing itself and protecting itself. When it was finally completed, the City decided that the Exxilons needed to be removed, drove them out and sealed itself up.

Thousands of the years later, Human and Dalek forces came to planet in search of Parrinium. The Doctor and Sarah Jane Smith also came to the planet by accident. All of their technology was de-powered by the city and they were trapped on the planet with the Exxilons. Despite this, the Daleks were able to modify their weapons, allowing them enslave the Humans and the Exxilons. The Daleks and the Doctor both realised that the City was the source of the energy drain. The Doctor and Bellal were able to get past the traps with their intelligence, while the Daleks simply survived anything the City threw at them. The Doctor was able to modify the City's computer, but he was chased out by the Daleks, who had also planted a bomb on the beacon. Due to the actions of the Daleks and the Doctor, the city overloaded and destroyed itself. (DWN: Death to the Daleks)