I think I want in on this. Here's my civ:
Civilization:Ri'Talan
City: Ri'Talan
Race: Humans and elves
Brief history: The city of Talan in the old world was a thriving center of arcane and druidic learning. The people lived in towers made of living redwoods, and lived in harmony with the surrounding forests. Their carefully-managed harvests of wood and game were supplemented with a great deal of trade with the outside world, mostly in rare herbs and magical goods. The final wars were disastrous to the city, however; even before the magical cataclysms that destroyed the world, they could no longer consistantly trade for food and were unable to support their entire population. When the rifts opened, Talan was a shadow of itself with perhaps half of its original population. Of these, perhaps half escaped.
The new world was not kind to the refugees. They could have thrived had they arrived in a forest, but instead they found themselves in the middle of a great savannah - not exactly a hostile environment, but one they were extremely ill-suited to. Their arcane knowledge was of little use without the critical tools and equipment lost to the fires of the old world, and the druids, unfamiliar with their surroundings, were little better off. They managed as best they could, though, and eventually settled on the banks of a great river, where the trees were slightly thicker and the game less scarce. Ri'Talan is still a struggling community, but the people have begun to adapt, and it's no longer one in danger of starvation.
Society:Talan was always a city governed by magic, with a council of wizards and druids at its head. Ri'Talan is somewhat different. The surviving councellors still hold some sway, but with their powers so heavily reduced, they're not nearly as influential as they once were. With survival uncertain, knowledge is less valued, and the new city's council has more representation from hunters and craftsmen than from magic-users. The people of Ri'Talan still yearn for their former greatness, but their magic is still weak, as more critical issues have been their immediate concern.
The people of Ri'Talan tend to be quite spiritual, in a druidic and nearly animist way. They have little interest in gods, believing that the old gods were left behind in the old world. Trees are fairly central to their traditions, and their scarcity around their new home is a major concern to the citizenry. (Logging is an always has been allowed, but is carefully planned and managed to maintain the health of the forest.)
Theme: Once-powerful spellcasters thrown into a world they're ill-suited to, now dependant on hunting to survive.