The original Silver Millennium is first shown during what is described as an ancient golden age, marked by peace, prosperity, and good relations between the people of Earth and the people of the Moon. The English dub of the anime states that the Moon Kingdom existed one thousand years ago, but in the original manga, it was prehistoric. Despite its name, the Silver Millennium appears to have lasted much longer than a thousand years. The Moon Kingdom itself was located in Mare Serenitatis (The Sea of Serenity) and ruled by Queen Serenity. It was also home to Princess Serenity and her four guardians, later to be known as the Guardian Senshi. According to the Sailor Moon R series, a second Silver Millennium is built on Earth some time between the 20th and 30th centuries, this time known specifically as Crystal Tokyo.
The royal family of the Silver Millennium bear special markings on their foreheads, shaped like small crescent moons. These may be seen on Queen Serenity, Princess/Neo-Queen Serenity, and Small Lady, as well as Sailor Venus when she was disguised as the princess, and the moon cats - Luna, Artemis and Diana. In the anime, non-royal civilians of the Moon Kingdom are shown without the symbol on their foreheads.
The Silver Millennium, though it had a fairy-tale appearance, is demonstrated to have been technologically advanced. It was located 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 Crown Prince of Earth during this era was Endymion, flanked by his four guardians. Relations between people of the Earth and the Moon were forbidden, but he and Princess Serenity fell in love anyway. Out of jealousy and under the influence of the evil Queen Metaria, a peasant woman named Beryl raised up the citizens of Earth in a war against the Moon, as a result of which both kingdoms were completely wiped out, so that the evolution of life had to restart from the beginning.
Before dying, the Queen sent her daughter and Endymion to be reborn on Earth during the 20th century. They become Usagi Tsukino and Mamoru Chiba and, even before their memories are intact, succeed in finding each other once again. The Sailor Senshi are reborn as well, becoming close friends; through their efforts, the reinstated Dark Kingdom and even Metaria herself are destroyed. In the manga, the Moon Kingdom and its castle are "resurrected" at the end of this conflict, but Usagi decides to continue living on Earth, with her parents and with Mamoru.
Later, in both the anime and the manga, it is revealed that a new Silver Millennium will exist in the 30th century, centered in the city of Crystal Tokyo. It will be ruled by Usagi and Mamoru under the names of Neo-Queen Serenity and King Endymion, and they will have a daughter named Princess Usagi Small Lady Serenity.
The Guardian Senshi are not only Neo-Queen Serenity's guardians, but guardians of the entire royal family. However, the location of the Outer Senshi, other than Sailor Pluto, is never mentioned. After their awakening in the manga, the Sailor Quartet also act as guards, but to Small Lady. Luna, Artemis, and Diana live in the palace as well.
At the center of the kingdom lies the Crystal Palace, which is where the Royal Family and the Guardian Senshi live. In the manga it is shown over water, while in the anime it is larger has another palace, Serenity Palace, located at the top middle spire. It is particularly shown in the beginning credits for the second opening sequence of Sailor Moon R, and is seen in a flashback where Chibiusa thinks that the Guardian Senshi and her parents have forgotten her birthday. Later, the interior is shown, indicating that this is the part of the Crystal Palace where the Royal Family and their protectors live.
Exposure to the Silver Crystal renders all of Crystal Tokyo's inhabitants functionally immortal. Anyone not born there becomes essentially locked at their current physical age, as shown by the Queen and King and their court, who all appear to be in their early twenties. Anyone born in Crystal Tokyo has a slow growth rate—Small Lady, for example, is stated in the manga to be over 900 years old, yet has the body and mind of child. According to her parents, such an extremely slow growth is irregular, and Chibiusa's extended childhood is an important part of the fourth plot arc.
The Sailor Senshi of the 30th century are depicted in their original uniforms, without any of the enhancements or powerups they are shown gaining in the latter part of the series. At the time the plot arc was drawn, Takeuchi had not yet introduced the idea of the Senshi's uniforms becoming enhanced.
In the anime, Queen Serenity makes her first appearance as a silhouette in episode 35, and is formally introduced in episode 44, when the Senshi are transported to the moon. (In the English dub, some footage of her talking with Artemis is shown at the beginning of the first episode.) Having sacrificed her own life long ago, she appears only in spirit, as a sort of hologram. It is she who tells the Senshi about their past lives, and about the history of the Moon Kingdom. In flashback, she is shown speaking the name of the Crystal (or, in the dub, "Cosmic Moon Power") to send her daughter and the others to be reborn in the future; she also uses Moon Healing Escalation, a power inherited by Sailor Moon. After this encounter, she appears just once more to give Sailor Moon a new transformation brooch and rod, and is mentioned again during the fourth story arc, in connection with Queen Nehellenia.
In the manga, Queen Serenity first appears in Act 10. Like in the anime, she appears as a hologram, and specifically mentions having saved her spirit within the computer, in order to preserve her will. She tells the Senshi of their past lives, which they begin to remember as she describes them, and tells them that they must find Metaria, who has escaped the seal placed on her and is hiding on Earth. Early on, Queen Serenity's spirit appears in the reconstructed Moon Kingdom, telling her daughter to find happiness with the one she loves. She appears three times more, all in flashback: once in Sailor Pluto's memories; after the birth of Princess Serenity, confronted by Queen Nehellenia; and visiting the Galaxy Cauldron.
In manga Act 41, the Sailor Team are revealed to be princesses of the Solar System. Each one had her own castle, which she is able to call upon late in the series for power. It is this act which first enables Sailor Moon to transform into Eternal Sailor Moon. The castles are named after moons, except for Mercury's and Venus'. Venus' castle is introduced long before the others', in the Sailor V manga, but she never mentions this to them.
In Act 45, Sailors Uranus, Neptune, and Pluto actually visit their castles, which are huge structures orbiting around their respective planets. Each is equipped with viewscreens, forcefields, comm systems, and other forms of high technology; each is also protected by a Power Guardian, who appears as a miniature version of the Senshi she serves. Sailor Pluto states that she remembers her castle, and that they were given to all the Senshi by Queen Serenity at the time of their birth.
Takeuchi's Materials Collection artbook shows the detailed design of each princess's unique gown. The gowns appear on the Senshi's bodies at key moments in the Stars manga, and are also pictured in the Original Picture Collection Volume IV. Flashbacks to the Silver Millennium, however, always show them dressed in their ordinary uniforms.
Each Power Guardian communicates with her respective Senshi by calling on the power of that Senshi's Sailor Crystal. They are able to help the Sailor Princesses call on the power of their Castles to produce a new transformation, such that they upgraded to new forms and poured this power into the Rainbow Moon Chálice, which in turn allowed Usagi to become Eternal Sailor Moon for the first time.
The Sailor Power Guardians disappear in the Stars arc around the time the Senshi they protect are killed. The exact nature of their fate is unclear, although the Senshi themselves are later reborn.
The Silver Crystal possesses tremendous power, capable of reviving an entire world from ruin, but the strain of using such power often costs the user her life - as the power is actually derived from the life force of the Moon dynasty, the members of which are the only ones who can actually use it. This is shown happening three times in the anime. The first time is in a flashback with Queen Serenity, and the second time is Usagi defeats Queen Metaria at the end of season one and finally, in the R movie. It is shown as the source of Queen Serenity's power during the Silver Millennium; Usagi Tsukino and Chibiusa each go on to inherit the Crystal in some form.
It is commonly portrayed in both the anime and manga as possibly the single most powerful artifact in the universe, able to focus the energy of its wielder to perform magnificent feats. However, there are several artifacts that rival it in strength, including the Black Crystal of the Death Phantom in Sailor Moon R and the Saffer Crystal of Sailor Galaxia. In the fifth series of the anime, the crystal also appears to double as the starseed of Sailor Moon, which reality was hinted at in the R movie, and the manga implies that it is her Sailor Crystal. It takes on a multitude of shapes, including round, diamond, rose, heart, star, and lotus, and at turns pink while stored within the brooches of both Sailor Moon and Sailor Chibi Moon.
Because Chibiusa comes from the future and will eventually inherit the Silver Crystal from Usagi, there are two versions of it present in the series. After the first and second story arcs, the crystals are kept in their respective transformation brooches and only removed in times of urgent need. In the final Last Dracul musical, a third Silver Crystal appears when Usagi's crystal resonates with a past version of itself, owned by Princess Serenity. This allows Serenity to briefly come to the present with her crystal and aid her future self. Before leaving, she states that the Silver Crystal cannot be used by just anyone. Vulcan later states that it will always find itself when it needs to.
Although criticism of Sailor Moon has included that her powers are gained from her "consumerist" external baubles, Emily Ravenwood notes that the Silver Crystal, which "saves the day", comes forth from Usagi's tear, and is therefore internal.
It was first used by Queen Serenity to remove negative influences from the Earth and also to send Princess Serenity and her court to Earth. It was also used to send the souls of her fallen subjects into the future to be reincarnated, which cost the queen her life. It also extends the life of the user and those around them if they do not use it to its limit.
It eventually evolves into the next form--a Sailor Crystal. For Sailor Moon, it evolved into the Silver Moon Crystal. For Chibiusa it evolved into the Pink Moon Crystal.
The Silver Crystal is also considered the most powerful crystal next to its evolved forms.
The Silver Crystal, however, was never used to remove any negative influences from the Earth.
These are the seven carriers of the Rainbow Crystals: