After the mine was depleted a use for the vast open pit was found. A city was built along the inside of the bowl, a park in the bottom, and a vast roof over the opening designed to allow sunlight into the depths while also harnessing solar power and melting winter snows into fresh water. Over 100,000 people inhabited the new city of Ulmazangrad for several decades.
Then the Unknown War hit. The survivors were never sure who had started it or who the possible enemy was. Most surviving settlements were thrown back into the dark age in the shadow of ultra technology of their ancestors. Almazangrad survived better than most, retaining most of its technology. It managed to survive the harsh winters of the aftermath as well. More knowledge survived in this city than anywhere else on the surface of the Earth.
However, Ulmazagrad had no heavy industry. While machines could be repaired and machine shops could create some parts, major replacements of technology were impossible. Over several generations technology did regress, but the depleted survivors were able to spread out from their hole when the harsh winters ended.
The flag represents the city's heritage as a diamond mining settlement.
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This week's flag was inspired by the real world Mir Mine, the flag of the city of Mirny, and by some rather ambitious plans to turn it into a city. In order to get a cool high-tech city the Empire was one created by Alexander or some Greek state back a few hundred years BC.
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Sean Sherman has been a fan of alternate timelines ever since seeing Spock with a goatee. By day he is a CPA, at night he explores the multiverse and shares his findings over at his blog, Other Times.