Silver Millennium

The Silver Millennium, though it had a fairy-tale appearance, demonstrated an advanced technology. The Moon Kingdom was located at the Sea of Serenity on the Moon. Silver Millennium was inhabited by beings with very long lifespans, whose mission was to help Earth people to progress. The princess of the Moon, Princess Serenity, was in love with Prince Endymion of the Earth. However, the people of Earth were corrupted by Queen Metalia and encouraged to hate and fear the people of the Moon. It existed within a dome which produced an artificial climate, and had an advanced computer called the "Eternity Main System". According to Artemis, ice skating was very popular there. Those who lived in the Silver Millennium had very long life spans and had two specific duties: First, they were to protect the Silver Crystal, an extremely powerful "holy stone" which had been handed down through the generations. Second, they were to watch over the evolution of Earth and protect it from any negative influence.

The Sailor Moon Series/Origin
Endymion, flanked by his four guardians, held the position of Crown Prince of Earth. Despite a prohibition on relations between people of the Earth and the Moon, he and Princess Serenity fell in love. Out of jealousy and under the influence of the evil Queen Metalia, a peasant woman named Beryl raised up the citizens of Earth in a war against the Moon. Warfare completely wiped out both kingdoms, so the evolution of life had to restart from the beginning. Before dying, the Queen sent her daughter and Endymion for rebirth on Earth during the 20th century.