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. It had no visible windows or doors.

The City was filled with traps which would kill anyone who was less intelligent or weak of mind. Underneath the City were root-like structures which hunted by sonar and killed any trespassers. If these methods didn't deter trespassers, the City could also produce humanoid anti-bodies.

The City was able to absorb all the energy from its surrounding, allowing it to perpetually repair itself. It could drain energy from the air and from the ground using its roots. 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. 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. Despite this, the actions of the Daleks and the Doctor were enough to overload the City, and it destroyed itself. (DWN: Death to the Daleks)