Rhodia was a planet, according to Charlie, "more beautiful than you could ever believe" and akin to "paradise". It was home to three billion people from two dominant species: the Rhodians and the Quill. (TV: For Tonight We Might Die)
Landscape
Red leaves seemed to be everywhere. The Quill inhabited the smallest of the southern continents. (TV: For Tonight We Might Die)
Miss Quill remembered Rhodia as a world of violent skies and hot sands. (PROSE: Joyride)
History
The Rhodians and Quill warred with each other, though each side remembered the reasons for the conflict differently. The Rhodians claimed the Quill mismanaged their economy and were resentful of the Rhodians' success; the Quill claimed the Rhodians ate up all the planet's resources, including that of the Quill. The Rhodians tried to help the Quill, but in the process made them so dependent that they could never recover.
The less numerous Quill rebels used war tactics described by the Rhodians as terrorism, though they thought of themselves as freedom fighters. One such tactic was bombing empty buildings. (TV: For Tonight We Might Die) Another tactic utilised was the deliberate transmission of misinformation about troop locations and food supplies to the Rhodians, to confuse them. The Quill would also transmit the videos of their successful conflicts to the Rhodians, making sure only to show the Rhodians killed in the fighting and not the Quill casualities. (PROSE: What She Does Next Will Astound You)
During the war, someone who was close to Andra'ath in some unknown capacity died. (PROSE: The Stone House)
The Rhodians won, ending the Quill's attacks and enslaving their captured leader, Andra'ath (later known as Miss Quill), with an arn, forcing her to become the protector of the Rhodian prince, Charlie. (TV: For Tonight We Might Die)
While the inhabitants of Rhodia were busy fighting among themselves, the Shadow Kin arrived and killed almost all of the three billion inhabitants - Rhodian and Quill. These casualties included the Queen of Rhodia and Miss Quill's sister, Orla'ath. (TV: For Tonight We Might Die, Nightvisiting)
Charlie and Miss Quill were the only survivors of the attack - the last of their respective species. They were rescued by the Twelfth Doctor and taken to Coal Hill Academy in 2016. (TV: For Tonight We Might Die)
Undated events
The plume priests of Rhodia once poured boiling water on themselves as an act of political protest. (PROSE: What She Does Next Will Astound You)
Culture
Parsela and Whitshade were fictional rebel heroes revered by supporters of a republic. (PROSE: The Stone House)
Miss Quill was aware of the Daleks, Gallifrey, the Time Lords, and the Last Great Time War. However, "Charlie Smith", the Rhodian Prince, was initially unfamiliar with the Daleks, whom he did not encounter until after Rhodia's civil war. (AUDIO: In Remembrance)
Customs
Apologising on Rhodia was, at least for Rhodians, a carefully regimented practice in which they would give an item of food to the person they were apologising to. The specific item would be determined by the nature of the action for which they were apologetic about. (PROSE: What She Does Next Will Astound You) After a meal, one was supposed to put the cutlery in a cross formation. (PROSE: The Stone House)
Science
The prames of the Renyalin changed according to weather, time and whoever was holding the aardvark. (PROSE: The Stone House) Rhodia also had a form of electronic information system similar to the Earth's Internet but significantly more advanced - and in Miss Quill's opinion, more superior. (PROSE: What She Does Next Will Astound You)